Rainbow baby question.

I have seen different things about a rainbow baby.

One is that your 5th born is called your rainbow baby.

Then another one I seen was a baby born after a pregnancy loss is a rainbow baby.

I have 3 living children they all were born after several miscarriages.

Oldest was born after loss of twin girls at 25 weeks and 2 first trimester losses.

Middle was born after a first trimester loss.

Youngest was born after 5 first trimester losses.

So are they all rainbow babies or just my 5th born if I get blessed to have that many?

Thank you