Yandex Disk is a cloud storage service provided by Yandex, which allows users to store files and access them from various devices over the internet. It offers features such as file synchronization, easy sharing of documents and media, and automatic photo and video backup. Yandex Disk provides users with a certain amount of free storage space, and additional space can be purchased through various subscription plans. The service integrates with other Yandex products and supports features like version history and secure file sharing.