The Language Server Protocol is essentially a standard for editors to talk to language tooling. All the usual refactor/go-to-definition/auto-complete functionality you expect from a modern IDE is implemented in a language-agnostic way in the editor in terms of calls to the language server, and language servers then provide the actual concrete implementations of that functionality.

IIRC Microsoft defined the spec in the context of creating VS Code, but these days every editor and their uncle supports it (from Vim and Emacs to Sublime Text and even IntelliJ). You can get a solid IDE-like experience for most mainstream-ish languages, and on most editors, through LSP.

Basically every editor decided it would be cool to be as slow as Emacs (said with love, as an Emacs user), and so now all the clever stuff is done in potentially several out of proc web servers, each of which uses gigabytes of RAM.

> The Language Server Protocol (LSP) is an open, JSON-RPC-based protocol for use between source code editors or integrated development environments (IDEs) and servers that provide "language intelligence tools":[1] programming language-specific features like code completion, syntax highlighting and marking of warnings and errors, as well as refactoring routines. The goal of the protocol is to allow programming language support to be implemented and distributed independently of any given editor or IDE.[2] In the early 2020s, LSP quickly became a "norm" for language intelligence tools providers.[1]

https://en.m.wikipedia.org/wiki/Language_Server_Protocol

thanks for asking! its what provides all language intelligence features in your IDE. so autocompletion, diagnostics, syntax highlighting etc. the postgres language server currently supports autocompletion, syntax error highlighting, type-checking and linting.