This article is from the Triathlon FAQ, by with numerous contributions by James Goddard others.
aerobars
a handlebar extension enabling the rider to use a more aerodynamic
position
bonk
running out of energy during a race a.k.a. hitting the wall
buoy
a float used to mark the swim course
blocking
riding in the passing lane
brick
a bike/run workout
drafting
the technique of riding in a pack during the cycling event
lemming start
a triathlon start where the competitors start one at a time
mass start
a triathlon start where all of the competitors start at the same time
instead
of in waves
roadie
a cyclist that does not to triathlons and hates triathletes
RST
rec.sport.triathlon
split
the time taken to complete an individual leg of a triathlon
transition
the period/area between legs of a triathlon where participants change
equipment/clothing for the next leg
T1
the swim to bike transition
T2
the bike to run transition
wave
a group of triathletes starting together as opposed to a mass start
 
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