A strait is a narrow passage of water connecting two seas Bi, the prefix, means two. Or the chemical symbol for bismuth.
Bi means 2 A strait or straits is a narrow, typically navigable channel of water that connects two larger, navigable bodies of water. It most commonly refers to a channel of water that lies between two land masses, but it may also refer to a navigable channel through a body of water that is otherwise not navigable, for example because it is too shallow, or because it contains an unnavigable reef or archipelago.
Or if you are talking about your homosexuality Bi- you like both genders Straight- you like the opposite gender and only that gender. Ex: boy only likes girl.