De rigueur (duh ree-GOOR) means required by custom or current fashion, something you're expected to do or have in a particular situation. It's a French phrase that literally means “of strictness.”

When something is de rigueur, it's what everyone considers necessary or proper in that context. In the 1800s, wearing gloves was de rigueur for wealthy women leaving the house. Today, wearing a costume might be de rigueur at a Halloween party, or bringing a gift might be de rigueur when you're invited to a birthday celebration.

The phrase usually describes unwritten social rules rather than actual laws. A tuxedo might be de rigueur at a fancy wedding, but no one will arrest you for wearing a regular suit. However, you might feel out of place or draw unwanted attention.

You can also use de rigueur with a touch of humor or gentle criticism. If everyone at your school suddenly starts wearing the same style of sneakers, you might say those sneakers have become de rigueur, pointing out how people sometimes follow trends without thinking much about them. The phrase recognizes that social expectations can be powerful, even when they're not written down anywhere.