Diploblastic and triploblastic are terms that describe
The number of germinal layers during embryonic development
Diploblastic animals have two germinal layers (ectoderm and endoderm) during embryonic development e.g. Poriferans. Triploblastic animals have three germinal layers (ectoderm, mesoderm and endoderm) during embryonic development e.g. Platyhelminthes.