Fetal age or Gestaintional age

lou

Hoping someone can explain this to me! If i am going off my LMP I am 7w4d. But due to a hectic month of April I know my conception date! So when I use online due date calculators including this app I am 8w0d but I just came across a website that said my Gestaintional week is 8w0d but my fetal age is 6w4d.. so does anyone understand this and know which one I should go by?