The term "awase" means wafuku (traditional Japanese clothes) with a lining. As a matter of practice, people wear it from October through May of the next year. However, some people wear it only in the middle of winter thanks to the increase of warm wafuku, such as wool-made ones, as well as the spread of heaters.
In the case of kosode (kimono with short sleeves) that has been used since the Muromachi period, 'awase' means the one that has a lining without cotton padding, and it is distinguished from a padded kosode for winter use.
Antonym : hitoe (a single layer of kimono)