Definition
An anti-cheat lives in the shipped game and runs after the player launches it. At startup it checks that the build and the things the game trusts still look right. While the game runs it keeps checking memory, the clock, input, and other values a cheat would change. A failed check means the game was modified, or a cheat tool is active. It does not rewrite the code before release.
Relevance
Cheats that change health, currency, or match results happen after launch. A runtime anti-cheat is how you notice them when the game starts and while it is being played. Obfuscation only hardens the build before you ship. It cannot see a cheat attached later.
Example
At launch, a check can refuse a build that no longer matches the one you shipped. While a match runs, another check watches health. A memory editor that freezes that value fails the check instead of counting as real health.
Connected
Synonyms
Cheat prevention, Tamper detection