Attire means clothing, especially the particular outfit someone chooses for a specific occasion or purpose. When an invitation says “formal attire required,” it's telling you to wear dressy clothes like a suit or fancy dress. When your soccer coach talks about proper practice attire, she means you need athletic clothes and cleats.

The word usually refers to complete outfits rather than individual pieces. You wouldn't call a single sock attire, but you might describe someone's entire hiking outfit as “appropriate mountain-climbing attire.”

Different situations call for different attire. Business attire means professional clothes like button-down shirts and slacks. Casual attire might mean jeans and a t-shirt. School often requires specific attire: some schools have uniforms, while others just ask students to dress appropriately.

The word carries a slightly formal tone. You're more likely to say “What should I wear?” in casual conversation, but an event organizer might write “Business casual attire recommended” on an invitation.