Here’s a definition of technical writing that I am going to use as part of a conference presentation:
A broad definition of technical writing: Any non-fiction writing of a technical or business nature. Sub-groups may include: Computer software and hardware documentation, process documentation, training materials, presentation materials, marketing materials, HR manuals, business plans, resumes and cover letters, engineering documents etc. A technical writer also translates technical jargon into English the rest of us can understand.
Alternate titles for a technical writer may include, copy writer, report specialist, documentation specialist.