Crypto glossary
Failed (reverted) transaction
A failed or reverted transaction is included in a block but undoes all its effects because a contract check failed; the network fee is still paid.
On Ethereum and similar chains, a transaction can be valid enough to be mined yet fail during execution. When a contract hits a condition it was written to reject, such as a require statement, it reverts: every change is rolled back as if nothing happened. The transaction still appears on the explorer with a failed status, uses up its nonce and charges the gas consumed until the revert.
Common causes in practice are slippage limits being exceeded because the price moved, an expired deadline on a swap, an insufficient token approval or balance, a mint that sold out, a contract that is paused, or running out of gas. Bots competing for the same opportunity often fail in batches, and many wallets now simulate transactions first to warn users before they sign. Other networks such as Solana also charge fees for failed transactions.
A failed transaction does not mean funds were lost beyond the fee, but users often confuse it with a pending or dropped transaction, which was never included. Reading the revert reason on the explorer usually shows what went wrong.
Example
A trader sets 0.5% slippage on a volatile token; the price moves 2% before inclusion, the router reverts the swap and the trader pays only the gas.