According to the different processing stages:
1 - Captured "comment":
It is a Facebook post, Facebook comment, blog post, blog comment, tweet, #hashtag, Youtube channel, Youtube video, or RSS that was captured because it matched with a search term loaded or it is a “comment” captured from a specific source loaded.
2 - Mention:
It is a Facebook post, Facebook comment, blog post, blog comment, tweet, #hashtag, Youtube channel, Youtube video, or RSS that after capture, entered in a entity (brand, product, campaign) of the Information structure because matched with a positive term.
3 - Opinion:
After entering in a entity, mentions are classified by sentiment (positive, negative, neutral) and after that, become in opinions.