:[N]bd[elete][!]
:bd[elete][!] [N]
Unload buffer [N] (default: current buffer) and delete it from the buffer list. If the buffer was changed, this fails, unless when [!] is specified, in which case changes are lost. The file remains unaffected. Any windows for this buffer are closed. If buffer [N] is the current buffer, another buffer will be displayed instead. This is the most recent entry in the jump list that points into a loaded buffer.
Actually, the buffer isn’t completely deleted, it is removed from the buffer list |unlisted-buffer| and option values, variables and mappings/abbreviations for the buffer are cleared.