SQL Structured Query Language A type of programming language used to construct database queries and perform updates and other maintenance of relational databases, SQL is not a full-fledged language that can create standalone applications--but it is strong enough to create interactive routines in other database programs. If you're looking into buying relational database software, make sure it has SQL support. Incidentally, SQL was developed as a result of an IBM project called Structured English Query Language, so to this day it is pronounced "sequel," not "squeal."