Definition of stacked
stacked can mean 2 distinct things. First, clarification that the cellar is the whole of our carpet. Whether it's chips in tournaments or money in games of cash games, the whole of what we have on the table is our basement. When we talk about stacked, we're talking about losing all of our chips, or when we take all of our opponent's chips ("I uncovered him on a cooler with aces against kings"). stacked also means protecting your chips when playing cash games. This technique is also called "ratholing".
An example of ratholing
For example, you buy the minimum possible on a table, say 50 euros. We double our carpet quickly to 100 euros. One leaves then the table to go to stacked. We go to the casino ticket office, exchange 50 euros of our chips for tickets and then take a seat at the same table with 50 euros. Some players want to protect their winnings this way. These players always prefer to have a small mat to go all in more easily. We call them the "shortstacks" specialists. Note that this technique is illegal almost everywhere and that online poker rooms have systems that will prevent you from doing so.