So you wanted to create a Custom Shape on photoshop but you started drawing a path because of the nature of what you were doing (or because you forgot to change the pen mode to Shape) and now when you want to right click > “Define Custom Path…” it’s disabled in the menu.
Here’s the solution:
1. Select the path with the path selection tool.
2. Go to Layer > New Fill Layer > Solid Color. (Or use the Create new fill or adjustment layer button in the layers palette)
3. You have turned a path into a new shape layer.