In the context of a large web application what many people describe as back end is hardly such. Typically that stuff is middleware. The actual back end would

In the context of a large web application what many people describe as back end is hardly such. Typically that stuff is middleware. The actual back end would be things like payment processing, database access, internal services, and so forth. The code sitting on a service that issues server calls and into the business logic that builds anything client facing is middleware. I call that stuff middleware because at a large enough company they would not let anything on a webserver go remotely close to anything storing data for security reasons. That being said fullstack doesn't actually mean the entire stack as the name would suggest. It really means the front-end plus the middleware, or both ends of HTTP. For developers experienced enough to write on both sides of HTTP it makes sense to tidy that up into a single position to lower labor costs.