Two different ways concurrent code goes wrong — one quietly hands back the wrong answer, the other never hands back an answer at all.
Both bugs only show up when multiple threads (or processes) are running at once, both are notoriously hard to reproduce, and both get lumped together as "concurrency bugs." But they fail in almost opposite ways. A race condition lets your program finish and return a result — it's just the wrong result, because two threads touched the same data in an order you didn't expect. A deadlockdoesn't return anything at all — the affected threads freeze permanently, each one waiting on a lock the other is holding. Confusing them means reaching for the wrong fix.