Definition
A baby that is conceived after a miscarriage or other loss of a baby.
Origins
In reference to a rainbow appearing after inclement weather.
How People Actually Use It
A baby born after the loss of a child. Examples: A child that is born alive and survives after a miscarriage, stillbirth or the death of a child of any age.
""Jordan is my rainbow baby 🌈. After the loss of my child I didn't think I could go on, but then I found out I was having a baby and I knew she was going to be someone worth sticking around for. I miss eldest child every day, but her rainbow baby sister carries on her name and we live on to make her proud.""
Source: Urban Dictionary