To call the minimum amount required in the first betting round in order to continue in the hand.
The minimum bet is the amount of the big blind. So, if the blinds are $1/$2, a player has the option to limp in for $2.
If all players have limped pre-flop the big blind has the option to check and see a flop without investing additional money.
An over-limp is when you limp after other player(s) have also limped into the pot.
EXAMPLE “With 7 other limpers, I decided to limp and see a cheap flop.”