The dead money poker term can mean several things. The first and more popular meaning is the one referring to all of the chips in the pot that aren’t part of any active player’s bet. The second meaning is when it’s used to refer to a player that has minimal winning chances.
In the context of the first meaning, a typical example of dead money is when a player misses a blind. When they do so, they have two options. They can wait until the big blind is theirs, or they can post all the previously owed blinds on the next hand.
The second meaning is used to refer to a player who is very weak or outmatched at the table, making them “dead money,” i.e. someone who is very likely to lose all of their chips.