Short Definition
A mutex is a synchronization primitive that allows only one thread or process to enter a critical section at a time.
Intuition
It is a one-person-at-a-time sign for shared data.
Technical Definition
A mutex provides mutual exclusion by requiring acquisition before accessing protected shared state and release afterward.
Example
Two threads updating the same counter can use a mutex to prevent lost updates.
Common Misunderstandings
A mutex prevents simultaneous access but can introduce deadlocks if used poorly.
Locking does not automatically make a whole design correct.