What is a 'getter' though? And what does it actually do? EDIT - Wikipedia [1] says it's a strip of (barium?) metal that is evaporated to react with any remaini

What is a 'getter' though? And what does it actually do? EDIT - Wikipedia [1] says it's a strip of (barium?) metal that is evaporated to react with any remaining gas/moisture particles in the tube and deposit them on the surface safely. It causes the shiny metallic film seen at the top of some tubes, I think? [1] https://en.wikipedia.org/wiki/Getter https://en.wikipedia.org/wiki/Getter