What is the Difference Between Similar But Different Things, Terms, and Objects

What is the Difference between Vitamin D and Vitamin D3

If cells are the bricks then vitamins are the cement for body. The need of vitamins of all types is so essential for the body that, if body lacks any one of them, it stops functioning properly and results in destruction of even major elements necessary for life. Vitamin D is one such element that is needed for the functioning of body.