This term is typically used when other designations such as "ex-step grandma", "godmother" "nanny", etc. are not accurately appointed.
For instance:Christina had a very special female mentor and friend during her teenage years, who helped her get through the death of her mother. When Christina had her own child, her mentor became Christina's child's Frandma.
Frandpa may be used for a male.
Frand-daughter or Frand-son may be used for the children.