Nexus - The website for download skyrim mods, alongside many other bethesda games. Can be found here.
Mod Manager - A program which allows for the quick installation and management of mods.
Load Order - Refers to the order in which your mods are loaded, where mods loaded later in the list will overwrite previous ones in places where they overlap. Can also generally refer to your plugin list.
MCM - Mod Configuration Menu, an in-game mod config accessed via SkyUI’s Mod Configuration window, allowing you to change some settings of your mods in real time.
Plugin - Refers to an .esp, .esl or .esm file. Required to make certain changes to the world, though simple texture and mesh replacers generally don't need one.
Conflict - An overlap between two mods. For example, two separate texture overhauls that overlap over a few textures. The one you want those textures from is the one that should load after.
Bashed Patch - An automated patch made by Wrye Bash that unifies leveled list edits, among other things.
USSEP - The Unofficial Skyrim Special Edition Patch's acronym. USLEEP is the Legendary Edition version.
BodySlide - A program used for editing body meshes and outfits for body replacer mods.
CBBE - A body replacer for females that allows for custom shapes through bodyslide.
3BA - A body replacer that works as an add-on to CBBE which adds physics.
UNP - A body replacer for females that has many different versions with varying shapes.
HIMBO - A body replacer for males that has many different versions with varying shapes.
SOS - Schlongs of Skyrim, a sex mod that is often used as a body replacer for males as well. Can also refer to many other mods; “SOS” is a running joke in the community.
HDT/FSMP - HDT-SMP (HDT's Skinned Mesh Physics) is a physics simulator for Skyrim. FSMP (Faster Skinned Mesh Physics) is the modern replacement which is faster, better and updated.
xEdit / SSEEdit - An advanced program for editing mod records and applying scripts.
ESP - A plugin type which counts against Skyrim’s 255 plugin limit.
ESL - A plugin type or flag with a more restrictive format which doesn’t count against the 255 plugin limit. Only available for SSE.
ESPFE - An ESP plugin that is flagged as an ESL, and as such does not count against the 255 plugin limit. Only available for SSE.
ESM - A plugin type or flag whose loose items don’t count against the Reference Handle Cap bug, and always loads early in the load order.
Port - A mod from LE made to work with SSE.
ENB - A massive shader modification which allows for huge lighting customization at the cost of FPS.
FOMOD - An interactive installer with choices and patches.
CC - Short for Creation Club, they are effectively Bethesda-endorsed and published paid mods. It is now replaced by Creations, which are made by modders and curated by Bethesda. It also includes all of the regular mods.
CK - The official Bethesda Creation Kit, a rather buggy program used for mod creation.
Feature Creep - When a mod edits things outside its scope in a way that isn't toggle-able or otherwise optional; e.g. A hat mod touching a perk tree.
Here is a modding dictionary with more. It is constantly expanding and being worked on.