What the word covers
Why the definition is contested
The strict reading includes everything: Ethereum, Solana, Litecoin, stablecoins, meme coins and tens of thousands of tokens nobody has looked at twice.
Two objections come up regularly, and both have a point.
The first is that Ethereum outgrew the category years ago. Calling a network with its own ecosystem an alternative to something else describes the history rather than the present.
The second is more practical and produces a common search query: are stablecoins altcoins? Technically yes, by the only definition the word has. Functionally no, because a token designed to hold a fixed value has nothing in common with an asset people buy hoping it appreciates. Anyone using the word loosely usually means the second sense.
The categories that actually differ
Grouping by what a coin does is more useful than grouping by what it is not.
Payment coins
Built to move value cheaply. Litecoin, Bitcoin Cash, Dogecoin. Low fees, fast confirmation, no ambition beyond transfer.
Smart contract platforms
Ethereum, Solana, BNB Chain, TON. These run programmable applications, and their native coins exist to pay for that execution.
Stablecoins
Track an external value. Included by definition, excluded by every practical purpose.
Privacy coins
Monero and a handful of others, where the ledger hides transaction detail by design.
Everything else
Governance tokens, meme coins, project-specific tokens. Thousands of entries, almost none with meaningful payment volume.
How many there are
How many exist
Tracking sites list tens of thousands, and the number is close to meaningless. Creating a token on an existing chain costs almost nothing and requires no permission, so the count reflects how easy issuance is rather than how much is being used.
The distribution matters more than the total. A small handful of assets carry almost all real transaction volume, and the tail consists of tokens with no liquidity, no holders and no activity.
Which ones matter for payments
Which altcoins matter for accepting payments
The list is shorter than the enthusiasm around the category suggests, and one question settles it: what do your customers hold?
Stablecoins dominate for the reason that always applies, which is that merchants want the settlement without the price movement. Among volatile coins, the ones that appear at checkout with any regularity are Litecoin, Dogecoin, Bitcoin Cash and the native coins of the fast chains.
Enabling an additional coin through a payment gateway costs a merchant nothing, so the sensible default is to enable what the gateway supports and let customer behaviour decide what gets used. Building a strategy around a specific altcoin is a different proposition and rarely justified.