buffer
also: buffer cache, I/O buffer, memory buffer
A temporary storage area in memory that holds data being transferred between processes, devices, or programs. Buffers allow data to be read in chunks rather than byte-by-byte, improving performance.
A buffer is a region of physical memory used to temporarily store data while it's being moved from one place to another—such as from disk to RAM, from one process to another, or from an application to a hardware device. Buffers act as intermediaries that smooth out mismatches in data transfer speeds.
For example, when you read a file from disk, the kernel fills a buffer with a block of data (say, 4 KB) rather than reading one byte at a time. Your program then reads from this buffer, which is much faster than repeated disk accesses. Similarly, when you type characters, they're buffered before being sent to a program.
Linux maintains several types of buffers: page cache (for file data), buffer cache (for block device I/O), and application-level buffers in user space. You can see buffer usage with commands like free -h or vmstat, which report memory allocated to buffers.