Super sets, tri sets? Whats up?

As i have just started taking training seriously again after a 8 year period of just going to the gym for cardio and light lifting there are terms that i am not sure what the meanings are.
Reading the recent m and f i see alot of super sets and tri sets. What is a super set, what is a tri set. Assumeing that a tri set is 3 sets but that didnt work seeing how they recomend 3-4 sets in the specific exercise.
Thanks for the help and the search option gave way too many results for a basic question,
Deltrain

Superset - Two exercises performed with NO rest interval.

Giant Set - More than two exercises performed with NO rest interval.

These are an advanced technique that can be safely used after about 6-12 months of serious training. Used too often, they can lead to overtraining. They are correctly used for hypertrophy (muscle growth). If strength is your goal than using longer rest intervals would be appopriate and different techniques - like forces reps.

thanks ;)