two overs means two over cards and its easy to have 18 or more outs for example:
your cards: As Ks
his cards: 2c 2h

Board: Ts 9s Jc
here you have 18 outs...9 spades, 3 queens (one is counted in the spades category), 3 kings and 3 aces= 9+3+3+3=18 outs


-anto