A query language helps machines talk with one another. It is a structured communication standard used to make requests to return information from a database. A query language allows developers coding applications to specify what they want a program to retrieve from an external service, in essence, "querying" information. Using a query language, applications can access, modify, or delete data from a database. SQL is likely the most well-known query language. Within the API space, GraphQL is a popular query language for communicating with multiple resources at once over HTTP.