placket

noun

1. the opening or slit at the top of a skirt, or in a dress or blouse, that facilitates putting it on and taking it off.
2. a pocket, especially one in a woman’s skirt.
3. Archaic.
   1. a petticoat.
   2. a woman.

noun dressmaking

1. a piece of cloth sewn in under a closure with buttons, hooks and eyes, zips, etc
2. the closure itself