Microsoft.PowerShell.Host.psd1

PowerShell data file Reference

A .psd1 file is a PowerShell data file. The file contains one table of keys and values in PowerShell syntax. The most common use is the module manifest, which describes a PowerShell module: name, version, exports, and dependencies. Localized message tables also use this format. The file contains data only, not program logic.

A file extension is only a part of the file name. It does not give a guarantee about the format or the content of a file. But on Windows, the extension selects the program that opens the file.