Definition of dunning
To raise means to add to what has already been bet. For example, if a player bets 10??? on the flop, we can fold (don't pay, but give up), call the bet for 10???, or raise (add more chips, to force them to fold or put more money in the pot). When we are preflop (before the flop), if we want to get into a hand, usually we will want to make a raise. Raising will decrease the number of players on the flop, which will increase our chances of winning the pot.
Further details on dunning
Unless you are in a "limit" variant you can always raise in poker. If a player raises to 3bb preflop and you want to raise to 10bb, you can. Your opponent can respond by raising in turn. A player can no longer raise when they have no chips left in their stack. If a player raises to 100??? for example, and that is his entire stack, he is said to be "all in" (his stack is all in the middle of the table) and the other players will have to call or fold from that point on.
