Definition of "yukata"

When made of lightweight cotton, the unlined and partially lined kimono become yukata. Yukata, however, do not have flutter sleeves, as they are considered too dressy for this informal kimono.

1988, John Marshall, Make Your Own Japanese Clothes: Patterns and Ideas for Modern Wear, Kodansha International, page 45

Most Japanese now wear yukata as summer kimono that are cool and comfortable.

2012, Amy Sylvester Katoh, Blue & White Japan, Tuttle Publishing