“Technical Communication” includes a number of disciplines, and not everyone agrees on the exact scope. For our purposes, let’s say it includes technical writing and illustration, aspects of information design, and aspects of instructional design.
Outputs can include manuals, user guides, and other materials. The target readership can include end users, maintainers, trainers, and support staff.
Of course, you might consider a service technician to be the “user” of a maintenance guide or parts list.