Seventeen terms every multichannel seller must master

Selling across several marketplaces at once carries a quiet trap: every platform speaks its own language. Amazon Seller Central calls one thing “fees,” MercadoLibre names it something else, and your 3PL emails you a report with columns nobody ever explained. You end up staring at three open tabs, an improvised Excel sheet, and the uneasy feeling that you’re setting tomorrow’s price with the day-before-yesterday’s numbers.

The problem is almost never a lack of data. If anything, there’s too much of it. The trouble is that it’s scattered, named differently in each place, and lagging in time. A seller who doesn’t own the vocabulary ends up comparing apples to oranges: they think a product is profitable on Amazon because they look at gross sales, without subtracting the category commission, the FBA cost, and the return that landed yesterday. The word you don’t understand is money you don’t see.

This guide walks through the seventeen terms that, in practice, separate the seller who guesses from the one who knows. It isn’t an academic dictionary; it’s the operating vocabulary you need to read any dashboard without translating in your head, and to make three different platforms finally mean the same thing when you bring them into a single source of truth.

the money terms: what you actually keep

Start at the end of the chain, because that’s where most sellers fool themselves. Gross sales (GMV, gross merchandise value) is everything that came in from sales before anything is touched. It’s the big, pretty number on the front page of any platform, and the most useless one for decision-making on its own.

From there you subtract the fees: the marketplace’s selling commission, the category commission, the shipping cost you absorb, the payment processing charge. On Amazon there’s also the referral fee and, if you use the platform’s logistics, the fulfillment fee. On MercadoLibre the logic is similar but the percentages and the names change. Adding these charges up wrong is the number-one mistake of the multichannel seller, because each channel presents them in a different format.

Then comes COGS (cost of goods sold): what the product cost you, landed in your warehouse. And only when you subtract fees and COGS from net revenue do you reach the number that matters: true net margin. Not the margin you imagine, but the one left after every player took their cut. A product can show a 40% gross margin and end up at 6% net once commissions and a batch of returns come in.

Dictionary: true net margin subtracts fees, COGS, shipping, and returns for each channel, not just the sale price.

the inventory terms: what you have and for how long

The second pocket of confusion is stock. The key phrase here is real available, and it almost never matches the number you see on a single platform. Physical stock in the warehouse isn’t the same as sellable stock: there are units reserved by in-flight orders, units in transit to the fulfillment center, and damaged or quarantined units the system still counts. If you sell the same unit on Amazon and on MercadoLibre because each panel tells you “there are 12,” you’ve just created an oversell and a cancellation that punishes your reputation.

That’s why it pays to think in terms of days of inventory (days of supply) rather than loose units. Twelve pieces mean nothing until you cross them against your sell velocity: if you sell four a day, you have three days left, and that’s an alert, not reassurance. Its sibling metric is the sell-through rate, the percentage of your inventory you actually sold in a period; it tells you whether you’re overbuying or running short.

Dictionary: days of inventory estimates how long your current stock lasts based on recent sell velocity, not on raw unit counts.

The term that closes this block is the stockout: running out of stock. It sounds obvious, but its cost is invisible in traditional reports, because a sale that didn’t happen shows up in no row. On marketplaces, a stockout costs more than the lost sale: it hurts your organic ranking and, on Amazon, can knock you off the Buy Box. Handling real-time inventory stops being a luxury once you understand that yesterday’s number is already stale by mid-morning.

the visibility terms: why you’re seen or not

Selling on a marketplace means competing for attention. Amazon’s Buy Box is the “Add to Cart” button when several sellers offer the same product: whoever wins it takes the large majority of sales. It isn’t won on price alone; your availability, your fulfillment method, and your history all weigh in. Losing the Buy Box without noticing is losing sales while your inventory sits there, untouched.

The discovery cousin of this concept is organic ranking: where you appear when someone searches, without paying for ads. It rises with conversion and sustained sales, and falls with stockouts, bad reviews, and incomplete listings. And here enters the conversion rate: of every hundred people who view your listing, how many buy. It’s the hinge between traffic and money, and the metric that fastest tells you whether the problem is the price, the photos, or the listing itself.

the advertising terms: what you pay to appear

When organic isn’t enough, you pay. And here live two acronyms worth not confusing. ACoS (advertising cost of sales) is the percentage of your ad sales that went to advertising: if you spend 100 on ads and generate 400 in attributed sales, your ACoS is 25%. TACoS (total advertising cost of sales) compares your ad spend against your total sales, not just the attributed ones; it’s the metric that reveals whether advertising is also pushing your organic, or whether you’ve become dependent on paying for every sale.

The mirror of ACoS is ROAS (return on ad spend): how much you get back for every unit invested. A ROAS of 4 means four in sales for every one spent. None of these three figures mean anything in isolation from your margin: a “good” ACoS on a thin-margin product can still run at a loss. That’s why advertising is never read alone; it’s read against the true net margin discussed above.

the operations terms: health and reputation

Some terms aren’t about money or marketing, yet they can take down a whole account if you ignore them. Fill rate is the percentage of orders you fulfilled complete and on time; your 3PL reports it and your marketplace watches it. The order defect rate bundles cancellations, claims, and chargebacks: on Amazon, crossing a certain threshold can suspend your account, no matter how much you sell.

And there’s lead time, the gap between ordering merchandise from your supplier and having it ready to sell. If your lead time is forty days and your days of inventory are fifteen, you’re already late even if you have stock today. Crossing lead time against days of inventory is what separates a planned replenishment from a panic run. A store like SPORTIFY, moving catalog on Amazon and MercadoLibre at once, lives or dies by how tightly it has these two numbers tied together.

Dictionary: real available is the stock you can truly sell today, after deducting reservations, transit, and quarantined units.

why a single source of truth changes the game

When each of these seventeen terms lives on a different platform, mastering them isn’t enough: you spend your day being a translator instead of a seller. The real change comes when all seventeen mean the same thing in one place, calculated with the same logic and updated in real time. There, Amazon’s true net margin is comparable to MercadoLibre’s, days of inventory consolidate across all your channels, and ACoS stops living in a separate tab.

That’s the entire point of consolidating your data instead of rebuilding it by hand every morning. If you want to see what this looks like in practice, check out how to read your dashboard in thirty seconds: the idea is for the vocabulary to stop being an obstacle and become a shortcut. Mastering these terms is the first step; having them calculated the same way, in a single board, is the one that actually gives you back hours and removes the uncertainty of deciding with old numbers.