Definition: "Decaf" is short for "decaffeinated" or "decaffeination." Contrary to popular belief, decaf is not the same as "caffeine free." Most decaf coffees and teas still contain at least trace amounts caffeine and (due to lack of enforcement of decaf health claims) some decaf drinks contain moderate amounts of caffeine or more.
While many herbal infusions (or tisanes) are naturally caffeine free, decaf teas are teas that naturally contain caffeine, but have had most of the caffeine removed.
Interesting side note: There is actually a naturally caffeine-free coffee out there. It's just very rare.
Also Known As: decaffeinated, decaffeination