Confused by the dress code for holiday parties? Join the club! But if you see semi-formal, it generally means this. For women, it’s a cocktail dress or a pants suit in a dressy fabric like cashmere, polyester or silk. For men, it’s a suit made of gabardine, cashmere, wool blend (not linen or seersucker, which are too casual). The suit can be worn without the vest.
As you can see, the fabric is very important. A cotton A-line dress is too casual for a semi-formal party, but a silk A-line dress will be fine (especially if it is accessorized with jewelry and an evening bag).