On YouTube profiles, the Quality Score tab shows an Average Duration value in the Audience Engagement Videos section (for regular videos) and another one in the Audience Engagement Shorts section (for Shorts). They tell you how long this channel's content typically is. The horizontal bars compare the value with channels of a similar subscriber count.
Calculation: the median video length in seconds of the last 12 videos (for the Shorts value: the median length of the last 12 Shorts). Using the median means that a single unusually long or short upload does not distort the value.
Unlike the other mini scores, the average duration is not part of the overall score and says nothing about the quality of the channel. It is a fit check: does the creator's typical video length match the format you have in mind, for example a short product mention versus a longer integration or a dedicated video?
TikTok profiles show a similar Average Duration value for the creator's videos. It helps you plan sponsored content that fits the creator's usual length; videos that are much longer or shorter than what the community is used to often do not match the creator's style.