The Kinsey Scale measures sexual orientation on a continuum from exclusively heterosexual to exclusively homosexual, with varying degrees of bisexuality in between. It is used to understand and categorize an individual's sexual attraction and experiences.

Homosexual: having a sexual attraction to persons of the same sex

Heterosexual: Sexually attracted to members of the opposite sex

Yes, that's the usual term. heterosexual = straight homosexual = gay

Not all men are homosexual. There are many men who are bisexual, homosexual, heterosexual, pan-sexual etc.

When referring to a straight girl you mean that she is heterosexual. If she is not heterosexual she may be considered homosexual or bisexual.