While working with Yandex. Audience, you may come across special terms:

Anonymous identifier (deviceid or cookie)
The unique identifier of the user's mobile app or browser. The ID becomes active when a user uses the relevant app or browser. As segments are updated, inactive anonymous identifiers are removed from the segments, and new ones are added (for example, if a user have purchased a new device or resinstalled an app), so that only anonymous identifiers that have been active in the past 30 days remain in the segments.
Segment reach
The number of found anonymous identifiers of users in the segment. Since one user can use several devices, apps, and browsers, the number of found users and the segment reach may differ.
Pixel reach
The number of found anonymous identifiers of users who have viewed ads containing the pixel.
Own data
User data provided by the advertiser: phone numbers, emails, and mobile device IDs. A file with own data must meet the requirements.
The number of own data file's entries for which anonymous identifiers have been found.