This question was inspired (at least in my head) by this wish question. Namely, wishing for higher levels.
One reason wishes for levels don’t work is because many DM’s say that a player is meta-gaming if they talk about "levels". But I wonder if levels are truly a abstract concept.
In game, a character would not understand things like experience points, hit points, ability scores, and terms like that. These are what I would call abstract–They are concepts we use as players to describe and work within the parameters of the 5e (and other systems) rules.
But levels have very specific traits attached to to them. The player gains more hit points, so yes, that part is still abstract and is reflected by the ability to withstand more punishment. But there are features that are determined (or even defined) by level such as extra attacks, new feats, ability to learn and use new spells. The list goes on. There is a direct correlation between these features/abilities and level.
In martial arts, there is the definitive marker of experience; the belt. In scouting there are merit badges. In the military there are ranks. These are what I would refer to as literal–proof of experience and training.
A 1st-level Fighter is a white belt, and a 20th-level Battle Master is a black belt and there would be stages in between. A 1st-level Ranger is a Cub Scout and a 20th-level Ranger is an "Arrow of Light". You get the idea.
So I’m asking, in 5e, is "level" (not XP) an abstract or a literal?