Definition of shortstack
Playing shortstack means that you have less than 100 big blinds. 100 big blinds is the benchmark. If you are playing at 100 big blinds, we say you have a full stack. If you have 250 big blinds we say you are deepstack, and if you have around 20 big blinds we say you are shortstack. There are two types of shotstack, the cash game shortstack which is a voluntary shortstack and the tournament shortstack which is an involuntary shortstack.
Shortstack in cash game vs shortstack in tournaments
If you always buy in for 20 big blinds in cash games, you may be a shortstack pro, a player who has perfected his shorthanded strategy. This shortstack player has decided to be a shortstack, he knows exactly what he is doing. When you have 20 or 10 or 5 big blinds in tournaments, it's not by choice; the hands haven't always gone our way. In these moments, we will feel the urgency to make a "move", that is to say to make an aggressive EV+ play to hopefully double or triple our stack. The shortstack in cash games and tournaments will not be the same type of player.