Available means ready to be used, obtained, or accessed when you need it. When the school library has a book available, you can check it out right now because it's on the shelf, not already borrowed by someone else. When your teacher says she's available after school for extra help, she means she has time and can meet with you.

Something becomes unavailable when it's used up, taken, or not accessible. Concert tickets might sell out and become unavailable. A person might be unavailable because they're busy with other commitments.

The word also describes how much of something exists for people to use. A scientist might study how much fresh water is available in a region. A business owner checks what products are available in their warehouse. When something is in short supply, people say there's limited availability.

Available means both existing and being ready and accessible right now. A basketball might exist in a locked storage closet, but it's not really available to you until someone unlocks the door. Understanding availability helps you plan: if your first choice isn't available, you know to have a backup plan.