Gear Level

Description
"Your Gear Level compared to the Unit Level of an enemy affects the damage you deal and receive against that enemy. Gear Level has no effect versus other players."

Summary
The so called "Gear Level" represents the general combat strength of a player, as the sum of levels of currently worn equipment (including weapon in hand).

It does not however, show how much damage you actually deal, as attributes are not affected by the gear level directly and vise versa.

It is also a rough estimate of the progression of a player, but does not display how many and which bosses have been slain.

Increasing the Gear Level
To increase ones gear level, better armours, jewellery and weapons need to be crafted.

Mechanics
Overall damage output to enemies (not players) is modified directly by Gear Level and is calculated by dividing a players Gear Level with an enemies Unit Level.

$$Damage % = {Gear \over Unit}$$

This basically means that if the Gear Level is for example double of that of an enemy, the player also deals double overall damage to them. If the Gear Level is half of that of an enemy however they would only deal half the damage to them.

Trivia
The current maximum (permanent) gear level is 84, by wearing a set of Blood Moon armour, a Blood Key and holding a Sanguine tier weapon. It can be temporarily increased to 85, by consuming Brute blood of at least 30% quality, which yields +1 gear level.