Semi-formal wear is a style of dress that's not highly formal and not completely informal; it falls in the middle of the two. Both men and women can dress in this style.
Wedding invitations may request that guests dress in semi-formal attire. Some appropriate options for women include a cocktail dress (such as a little black dress), a dressy suit or a dressy skirt and top, taking into consideration the season.
Men can't go wrong with a dark-colored business suit, a dress shirt, a tie, leather dress shoes and dark dress shoes. For a daytime semi-formal wedding, another appropriate option may be a stroller, which is an ensemble, usually dark gray, resembling a relaxed version of the morning dress style.