(+ object)
The tank divisions overran the countryside.
The city was being overrun by enemy troops.
Rats overran the ship.
In the summer, the town is overrun with/by tourists. (=is filled with tourists)
2 : to run or go beyond or past (something)
The runner overran (=ran past) third base.
The plane overran the runway.
The stream has overrun (=overflowed) its banks.
His speech overran the time allowed.
3 : to spread over or throughout (something)
Weeds overran the garden. = The garden was overrun with/by weeds.
Crime overran the neighborhood.