SSE
In plain terms
A method for servers to push updates to browsers over HTTP.
Going deeper
Server-Sent Events let a server stream a one-way sequence of updates to the client over a single long-lived HTTP connection. It's simpler than websockets for one-way data.
Under the hood
Unidirectional (server→client) and auto-reconnecting; lighter than websockets for streaming notifications.
Examples
Live feeds, notifications, streaming updates, dashboards, EventSource.
Think of it like...
Like subscribing to a live news ticker that the server keeps updating.