A partition in SQL is a way of dividing a large table into smaller, more manageable pieces. Each partition is essentially a separate table that contains a subset of the overall data. This can help improve query performance, as queries can be run on individual partitions rather than the entire table. Partitions are typically defined based on a specific column or set of columns in the table, such as a date range or geographic region. The partitioning scheme can be specified when creating a table or added later using ALTER TABLE statements.