Work in progress
A plugin is a file used to load game data into the Creation Engine games. The file can usually be identified by the file extension of ESM, ESP or ESL. Skyrim Special Edition and Fallout 4 also support a unique type of plugin know as an ESLP (sometimes called an ESPFE) which has the regular ESP file extension but behaves more like an ESL file when loaded by the engine.
While the file extension can be useful to define which type of plugin you are dealing with, it doesn't always give us the full picture. Plugin files are compromised of a header and a set of records. The header contains the properties and metadata of the plugin, whereas the records refer to in-game objects (e.g. NPCs, dialogue, items).
Grouped by types or record, hexidecimal IDs, referencing other plugins (overwrites)