Casual Shirt
Casual wear (or casual attire or clothing) is a Western dress code that is relaxed, occasional, spontaneous and suited for everyday use. Casual wear became popular in the Western world following the counterculture of the 1960s. When emphasising casual wear's comfort, it may be referred to as leisurewear or loungewear.
While casual is "informal" in the sense of "not formal", informal wear traditionally refers to a Western dress code associated with suits—a step below semi-formal wear—thus being more formal than casual attire.