Two long or cylindrical objects — the counter '本' used for counting long, thin items. A very common everyday expression for 'two (of something long)'.
鉛筆を二本貸してくれますか？
Could you lend me two pencils?
ビール二本とサラダをお願いします。
Two beers and a salad, please.
彼は靴下を二本同時に買った。
He bought two pairs of socks at the same time.