here for all you old people who dont know how to google:
Compared to cash games, tournament holdem poker is notably different by the fact that you need to increase your stack in order to survive, whilst in cash games if you maintain a constant stack for hours, you are not winning but you are not losing either.
In order to convey this notion of variable chip value, Paul Magriel coined the term M factor, originally conceptualized by Doyle Brunson in Super System and later popularized by Dan Harrington in Harrington on Hold'em.
The M factor is simply equal to stack/(small blind + big blind + total antes), where total antes is the value of the ante times the number of players at the table.
The denominator of this fraction is the total number of chips it costs to stay at the table for one orbit, so M is the number of orbits you can survive without taking into account any action that you could make. Equivalently as the pot before any action is the blinds plus all antes, M is your stack counted in number of starting pots.
You must have played some Texas Hold'em tournaments in order to appreciate how crucial this M factor can be. This corresponds to the familiar feeling of being eaten alive by the rising blinds and antes when your stack is small and M is small too.
now admittedly im not i fully understand it, but at least its a definition