A busk is the metal "hook and eye" closure you see on the front of some corsets. A busk is a great convenience for wearing a corset, but it is a personal choice, and it is by no means required. If you choose not to have a busk, you will have to unlace your corset, taking the strings almost completely out of the grommets, then re-lace your corset through the grommets every time you put it on. With a busk, all you will have to do is loosen and tighten the laces, without removing them from their grommets. Saves a lot of time, especially if you wear your corset regularly.
Your busk will come with an "underbusk." An underbusk is a flap of fabric UNDERNEATH the busk that hides the gap in the front of your corset. Without an underbusk, you would be able to see skin or clothing peeking out in between the two halves of the busk. An underbusk hides this. It's about 3/8" in width, and it's flush with the corset on the inside so it doesn't rub or cause discomfort.
Some people don't like the way a busk looks, either because of the metal hook and eyes show, OR because they have a pretty pattern in their fabric that they don't want to break up on the center front panel.
HOW IT WORKS: A busk will make it much easier and faster to get in and out of your corset. It's a time saver, and makes life easier when you wear your corset frequently.