Buffer is a temporary storage area, usually a block in memory, in which items are placed while waiting to be transferred from an input device or to an output device. It is mostly used for input/output processes.
As an example, if you were to print a long document, you would not want your CPU waiting around asking your printer “Are you ready for another paragraph?” Instead, the CPU will fill a memory buffer with the document’s data, instruct the printer to print the buffer contents, and go back to its other business.
Buffer is also sometimes called as - Buffer cache.