That said, the names are becoming increasingly unspecific. Many schools run an associated "nursery" which is targetted exclusively at children over 3 intended to attend that same school. "Playgroup" is increasingly used to describe parent and toddler groups (which are mostly intended for under 3 year old children).
If you are trying to decide on a preschool or childcare place, the best thing to do is to ignore the nomenclature, and simply treat each provider as an individual service provider, asking them what they think they do and what they can do for you and your child.