The representation of a file loaded into memory. Edits are performed on buffers.
This tag is for questions about interacting with Vim's buffers.
From :help windows-intro
A buffer is the in-memory text of a file
...
A buffer is a file loaded into memory for editing. The original file remains unchanged until you write the buffer to the file.
For questions about Vim windows (the "viewport" onto a buffer) see window-management.
Buffers and windows are coupled topics. For more information about both, see :help windows.txt