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1.
1. The epic and unparalleled event of taking multiple alcoholic shots, the number of which is significant (ie. years of marriage, number of V-cards taken, etc.), in order to expedite the process of pregaming. The use of a theme song is highly recommended, though not required.

2. The act of progressing.
"Dood, Timmy just took a 13 shot progression for his frat's 13th anniversary and now he's puking in the bathtub."
by Meesch April 18, 2013
 
2.

1. A gradual change or advancement from one state to another.

2. Movement forward or onward

3. A series or succession of related things.

4. A sequence of numbers or terms in which each can be derived from its predecessor using a constant formula.

Progression can be good as well as bad.
by Jafje September 05, 2007