A man who sits in a congress — a law-making body — and, in the English learners meet most, a man in the United States House of Representatives. News, votes, and letters to “your congressman” almost always mean that House, not the Senate. Though actually Congress as a whole is two rooms: the House and the Senate. A member of the Senate is a senator, even though the Senate is part of Congress. Other countries have a congress too, but school English nearly always points at the US. The word is ordinary news English, not slang. Many people now prefer representative or member of Congress, because -man leaves women out — and because a voter may not know, or may not wish to mark, the person’s gender.