Meteor currently uses MongoDB by default to store data on the server, although there are drivers planned for use with relational databases too.
Note
If you are adventurous, you can try one of the community-built SQL drivers, such as the numtel:mysql package from https://atmospherejs.com/numtel/mysql.
MongoDB is a NoSQL database. This means it is based on a flat document structure instead of a relational table structure. Its document approach makes it ideal for JavaScript as documents are written in BJSON, which is very similar to the JSON format.
Meteor has a database everywhere approach, which means that we have the same API to query the database on the client as well as on the server. Yet, when we query the database on the client, we are only able to access the data that we published to a client.
MongoDB uses a data structure called collection, which is the equivalent of a table in a SQL database. Collections contain documents, where each document has its own unique ID...