Essentially, a teaser, sometimes called a dropper, is a second, small, low weight "lure" of some type used to increase chances of hookups. Most often, the teaser is a fly but it can also be a small or light plastic like a Red Gill...
Here was an interesting thread by a lot of serious anglers from last year debating the use of teasers and how to rig them.
http://www.striped-bass.com/vbulleti...ghlight=teaser
Also, don't be afraid to run teaser through the search feature of the message board....