This is that thing where a segment is drawn across a triangle, parallel to one side while hitting the other two sides in their midpoints.
Medians, Centroids & Orthocenters
This video covers a grab bag of fun geometry terms, including the circumcenter. Most of this stuff you'll never see again, but it's kind of cool that the centroid of a triangle is also it's center of gravity, or balance point.
If you do not have an account, you should get one, because it is awesome! You can save a playlist for each test or each chapter, and save your "greatest hits" into a "watch right before the final" list (not that we recommend cramming, but when in Rome...)