Buffer
In plain terms
A temporary storage area for data in transit.
Going deeper
A buffer holds data temporarily while it moves between processes or devices operating at different speeds, smoothing flow. It absorbs timing mismatches.
Under the hood
Decouples producer/consumer speeds; overflows (buffer overflow) are a classic security risk.
Examples
I/O buffers, video buffering, network buffers, producer-consumer.
Think of it like...
Like a waiting room holding people until the next stage is ready for them.