ELI5- What are blood groups? Why do they differ from person to person? Why can’t a person of one blood group receive blood from a person of a different blood group?

Question

Edit: Whoever it is, thank you very much for the silver! This the first award I’ve recieved on Reddit! I love you!

Edit: Whoever gave me the gold… You’re a legend! You’re a fucking legend!! Thanks a lot Redditor!! It means a lot!

In: Biology

Answer 1

What about Rh+ and RH-? What do those mean?