In software, a deadlock is a situation where two or more processes or threads become stuck in a way that none of them can proceed with their execution. It's a scenario where each process is waiting for a resource that's held by another process, creating a circular dependency, and as a result, none of the processes can make progress.

Here's a simplified explanation of a deadlock:

Imagine two people, Alice and Bob, sharing a single bathroom with two doors. Each person needs to use both doors to access the bathroom. Now, if Alice enters through Door 1 and locks it behind her while trying to open Door 2, and at the same time, Bob enters through Door 2 and locks it behind him while trying to open Door 1, they both become stuck. Alice can't open Door 2 because Bob has locked it, and Bob can't open Door 1 because Alice has locked it. They're both waiting for the other to release the lock, but neither can do so, resulting in a deadlock situation where no one can use the bathroom.

In software terms:

Processes or threads are like Alice and Bob, each trying to access resources (e.g., memory, files, database records) that are locked by other processes.
When a process can't proceed because it's waiting for a resource that's held by another process, and that other process is also waiting for a resource held by the first process, a deadlock occurs.
Deadlocks can lead to a complete halt in the execution of a program, causing it to become unresponsive or "dead."

Deadlocks are a significant concern in concurrent or multi-threaded programming and can be challenging to detect and resolve. To prevent or handle deadlocks, developers often use techniques like resource allocation strategies, timeouts, and deadlock detection algorithms to gracefully recover from such situations and allow programs to continue running.