Coif is a type of hat that people used to wear a very long time ago, back in the olden days before we had electricity or phones or cars. It was made from cloth or other soft material and could be worn by men or women.
The coif was a special hat that covered the whole head and neck, kind of like a hood. It was often worn by people who needed to keep their hair out of their faces while they were working, like farmers or blacksmiths, or by people who wanted to look fancy, like fancy ladies who were going to a party.
Some coifs were very simple, with just a plain design, but others were fancier and might have ruffles or lace or even jewels on them. Coifs were very popular for a long time, but now we don't wear them very often anymore because we have other, more modern ways to keep our hair out of our faces. But they are still fun to learn about!