There is only one file type that uses the .LINQ extension:
LINQPad Query File
A LINQ file is a text file created by LINQPad, a utility that helps .NET Framework developers test code outside of IDEs like Microsoft Visual Studio. It typically contains a query in the LINQ (Language Integrated Query) query language that interactively queries data sources, such as SQL, SQLite, Oracle, MySQL, Postgres, or OData. LINQ files may also store a C#, F#, Visual Basic (VB) expression, statement block, or program.
Updated: December 22, 2019