Language Integrated Query (LINQ) is a Microsoft .NET Framework component that adds native data querying capabilities to .NET languages, although ports exist for Java, PHP, JavaScript and ActionScript.

Description is taken from Wikipedia:

LINQ defines a set of method names (called standard query operators, or standard sequence operators), along with translation rules from so-called query expressions to expressions using these method names, lambda expressions and anonymous types. These can, for example, be used to project and filter data into arrays, enumerable classes, XML (LINQ to XML), relational databases, and third party data sources. Other uses, which use query expressions as a general framework for composing readable arbitrary computations, include the construction of event handlers or monadic parsers.