BizSugar.com › Social Media › YouTube Video Annotations

Video Annotations are text commentary that you add to your videos. You can use them to add background information, link to related videos, create an interactive element, or add call-to-action to your videos.
Strictly speaking, Annotations are NOT a direct SEO strategy – the words that you add to your video are not indexed by the search engines. However, viewer engagement or interactions are measured by the search engines, and Annotations can be used to increase those interactions.