Shorty wetsuit is a summer wetsuit and it is the lightest wetsuit model there is. It is meant for summer surfing and surfing in warm waters. You can start using it when the water temperature drops to around 72F/22C or when you simply feel cold because of the wind, cloudy weather, rain, lower air temperature etc… If the water has higher temperature you generally don’t need a wetsuit at all, you can wear a wetsuit top or a vest. But everyone knows for himself how sustainable to cold he is.
Shorty is called shorty because of the short sleves for arms and legs. This leaves your arms and legs exposed. Neoprene thickness in this wetsuits is usually 2 millimeters and a lot of times it has flatlocked stitches which are not waterproof. But in the summer warm water that doesn’t really matter.