What is a .unityproj file ?

Hello,
I have to send a *.unityproj to someone but I dont even know what is it and how can we get this file.
Someone could explain me ?

It is an xml file with configuration project data used by either MonoDevelop or Visual Studio.

You will see it referenced in the Assembly-CSharp-firstpass.csproj file in your project folder.

And it is relevant in the most current version of Unity.