[ C ] something or someone that helps protect from harm:

[ C ] the metal parts at the front and back of a train or at the end of a track, that help protect the train and reduce damage if the train hits something

[ C or U ] a chemical that keeps a liquid from becoming more or less acidic

[ C ] an extra supply of materials that a company keeps in order to prevent a situation where none are available:

[ C ] UK old-fashioned a silly old man:

[ T ] to provide protection against harm

[ I or T ] When a computer buffers information or buffers, it stores information temporarily in its memory while dealing with it or sending it.