I somehow now have this in my startup file. Can someone tell me what this represents and how to change/remove it?
That is the unit you're using in your current project, it is set from the scene tab (see image below), to set it to how it is by default you have to select Meters in the tab where it says Miles and then set the length to None. Basically, you chose Feet as the default lenght to work with so every square in the blender grid is 1 feet long to you. In the Scene tab you see below you can choose which unit to use when you work which can be pretty useful if you want to do things precisely.