SQL (Structured Query Language) is a programming language used for managing and manipulating relational databases. It allows you to insert, update, and retrieve data stored in a database, as well as create and modify the database schema (i.e. tables, columns, and relationships between tables).

Here are some basic SQL commands:

• SELECT: used to retrieve data from a database
• INSERT INTO: used to insert new data into a database
• UPDATE: used to modify existing data in a database
• DELETE: used to delete data from a database
• CREATE TABLE: used to create a new table in a database
• ALTER TABLE: used to modify an existing table in a database
• DROP TABLE: used to delete a table from a database

SQL is used by many popular databases, including MySQL, PostgreSQL, Microsoft SQL Server, and Oracle.