Configs refer to the configuration files which are used by the game to quickly change game parameters, such as graphics options. Many configs are designed to improve game performance through lowering graphics settings, as well as providing extra functionality through use of client commands, such as viewmodel_fov and interp settings.
FPS configs strive to lower game graphics as much as possible in order to increase the framerate (FPS) of the game. Popular graphics configs include Chris's Highframes, Maxframes, and Dx9frames, while configs such as m0reframes have been used in the past.
Comanglia's FPS Config - The go to config for most competitive tf2 players who need more frames. It's considered by many to be one of the most effective configs current available.
TF2Mate - TF2Mate is the most popular config generator amongst the TF2 community. It allows players to configure their graphics settings, binds, and also comes with a crosshair switcher that allows the user to pick their own crosshair for each weapon slot on each class.  - CFGen is a less popular config generator, allowing you to only choose between Comanglia's FPS configs, weather you use windows or full-screen, if you want custom configs such as offline rocketjumping config, automatically record games, custom files such as remove bullet-hole dust, viewmodel settings, damage indicators, network settings, and custom binds.
Chris' Configurations - Chris' Configurations, or, simply "Chris' Configs," are FPS configurations of which, up until recently, was maintained by Chris. This config is highly popular and is used most of the time by TF2 competitive players. Chris' Configs come in several different versions, the most popular of which is the "maxframes config", which gives the maximum framerate possible while at the same time reducing the quality of the textures and the overall look of TF2. Alternatively, players can go for the "Highframes config", which makes TF2 look a little better compared to "Maxframes" but at the expense of not getting the maximum possible framerate.
m0re FPS Configurations - m0re FPS Configurations is the FPS config which pales in comparison to Chris' Configs due to performance but is a healthy alternative to Chris' Configs.
Rhapsody's Performance Config - an updated version of Chris' dx9frames config created by RhapsodySL. Gives higher frames than Chris' version did with some extra features such as ingame config setting managing, among other things.
Green Dolphin Config - A super-low FPS config for people who like blocky textures.
Transparent Viewmodels - Makes your weapon viewmodel's transparent
Improved Crouch Jump Script - a simple script that lets you press space once to jump then keep holding space to crouch.
Semi Comp Medic Config - A bare bones Medic Config with the essentials for playing medic at a higher level.
Helpful Spy Scripts by Stabby Stabby - A set of scripts created by Competitive Spy Stabby Stabby for spy.