To limp after one or more players has limped into the pot before you.
For example. The blinds are $1/$2. If two players limp in for $2 in a no-limit hold’em cash game and then a subsequent player in the same pre-flop betting round also just calls the $2 on the button, then he/she is said to have overlimped.
It is usually done with speculative hands that have good implied odds.