Customary means following the usual way of doing things, the established traditions or habits of a group. What's customary in your family might be taking off your shoes at the door, while in your friend's house it might be customary to leave them on. What's customary changes depending on where you are and who you're with.

In Japan, it's customary to bow when greeting someone. In many American schools, it's customary to raise your hand before speaking in class. These aren't strict laws: they're the normal, expected ways people behave in particular situations. When you follow what's customary, you're doing what people in that situation would do.

The word often appears when someone wants to emphasize a traditional approach: “It's customary to send a thank-you note after receiving a gift.” This doesn't mean you'll get in serious trouble if you don't, but it suggests that doing so shows you understand and respect the tradition.

Customary comes from the word custom, meaning a traditional practice. When something happens regularly enough, it becomes customary. If your class always starts with silent reading, that five minutes of quiet has become the customary way to begin the day.