This article is from the Birds FAQ, by Lanny Chambers with numerous contributions by others.
Many people who are interested in birds find it useful to keep a list
of the species they have seen: a "life list." Doing so helps them to
remember their encounters with birds, and thus makes them better
prepared to identify those birds in the future. Consider creating one
of your own; if you do, you'll enhance its usefulness if you include
the dates and locations of your sightings.
The term "lister" refers to a person who particularly enjoys the sport
of seeing as many bird species as possible within defined geographic
areas. So a lister might have a North America list, a backyard list,
a Kentucky list, and a Sweden list. Sometimes the term is used
pejoratively to imply that someone's interest in the natural world is
superficial. Do not make this implication on rec.birds (see section