- a person sentenced to or serving a term of life imprisonment.
- a person committed to a professional lifetime career in the military.
- a person who has devoted a lifetime to a profession, occupation, or pursuit.
- (in birding)
- a species of bird not seen previously and that will therefore be added to the bird watcher's life list.
- the sighting of a bird of a previously unseen species: It seems like forever since I've had a lifer!
- a prisoner sentenced to life imprisonment
