When selecting bridesmaids, it can be confusing what roles each should be. In general, maid of honor is a bridesmaid you select as the chief bridesmaid whom usually will be responsible for organizing bridal showers and such. You'll want to select someone responsible and is good at organization. Maid of honor is the title given for someone not married. If it's someone married, then their title/role will be matron of honor.
For the bridal party, a bride will sometimes select a male attendant to be their honor attendant, which will be called man of honor and some uses the terms bridesman. Similarly for a groom to select a female in honor would be best woman.
maid of honor = female bridesmaid selected as the chief/honor attendant.
matron of honor = basically a maid of honor but married.
man of honor = bride selects a male as the role of maid of honor.
bridesman = bride selects a male friend as attendant.
groomsgirl = groom selects a female as groomsman role.
best woman = groom selects a female as role of best man.