- snapshot = an exact capture of what a volume looked like at a particular moment in time, including all it's data.
- image = a total snapshot of a system (doesn't save the user data)
In OpenStack, an instance snapshot is an image. The only difference between an image that you upload directly to glance and an image you create by snapshot is that an image created by snapshot has additional properties in the glance database.
So why does OpenStack distinguish images from snapshots?