The Glowing effect causes entities to glow with an outline that can be seen through blocks and entities. This outline is white by default, but can be set to display other colors if the entity is part of a team (the color being the color of the team). The outline displays around any holes in a mob's texture or model, though only when that part of the model can be seen all the way through. If multiple entities with glowing are near each other, the outlines merge to prevent overlapping/Z-Fighting.
This does not affect mob models as seen in the inventory, of either the player or ridden mobs.[1]
The source of the effects is irrelevant for the purposes of this advancement. Other status effects may be applied to the player, but are ignored for this advancement.
This is a hidden advancement, meaning that it can be viewed by the player only after completing it, regardless of if its child advancement(s), if any, have been completed.