Hi there,
Root motion is a technique in which the translation and rotation are baked into the animation file resulting in a more precise movement. It is more used for animation montages, such as jumps, rolls, climbs, dashes and attacks. For locomotion, it was technically replaced by other methods, such as Root Motion extraction to curves and Motion Matching/ Distance Matching.
A few resources for you:
Should You Use Root Motion? - YouTube
Example:
Ue4 - Root motion controller / RnD test - YouTube
Two playlists:
Distance Matching