A loose analogy is, “Meteor is to Node as Rails is to Ruby.” It’s a large, opinionated framework that uses Node on the server. Node itself is just a low-level framework providing functions for sending and receiving HTTP requests and performing other I/O.
Meteor is radically ambitious: By default, every page it serves is actually a Handlebars template that’s kept in sync with the server. Try the Leaderboard example: You create a template that simply says “List the names and scores,” and every time any client changes a name or score, the page updates with the new data—not just for that client, but for everyone viewing the page.
Another difference: While Node itself is stable and widely used in production, Meteor is in a “preview” state. There are serious bugs, and certain things that don’t fit with Meteor’s data-centric conceptual model (such as animations) are very hard to do.
If you love playing with new technologies, give Meteor a spin. If you want a more traditional, stable web framework built on Node, take a look at Express.