Edge typically means that the software is running neither on an end device (e.g. a consumers phone/PC/tablet/TV), nor on the very backend in a big datacenter (like AWS us-east-1 or another region), but somewhere in between. E.g. a "mini-datacenter" close to the user (CDN points-of-presence (POPs) are called edge locations", or some aggregation points in between (e.g. gateway devices in factories that proxy between on-site components and in-cloud components).

The term doesn't have a lot to do with how efficient or non-efficient the software that is run in those places is.