The spotlight is a Pro-only feature that lets you feature certain scores on your profile.
If you have a Pro account, then among the options available under the ⫶ menu on the right of each of your score pages, there is an "Add to spotlight" link (after this link is clicked, it becomes a "Remove from spotlight" link). While free accounts have a total limit of five scores, the spotlight lets you put up to five scores at the top of your profile, with the rest below in order by upload date (most recent first). This does not affect the categorizing of your scores in any other way.
If you already have five scores in the spotlight, then adding another will automatically remove the oldest one.