Something chartered is rented or leased for a short time. A chartered bus is sometimes used to take a class of kids on a field trip to the zoo.
When you charter something, you use it for a specific length of time and pay a fee for it — and when you've done this, it's chartered. Most chartered things are vehicles of some sort, like a chartered airplane or a chartered yacht, used by a group of people who are traveling together. Chartered and charter come from the Latin chartula, "little paper," as in the paper form you fill out when you charter something.