Inside Sales is a term coming from the late 1980s to differentiate complex sales processes from telemarketing. As telemarketing relies on predefined scripts, the inside sales process is much more complex. Besides, Inside Sales doesn’t rely on telephone so much, but instead successful inside sales reps use a bunch of tools to share their screen and conduct conference meetings.
In the 1990s the term Inside Sales was used to differentiate from Outside Sales, because inside sales reps usually stay in the office and don’t go to customers. These days, increasingly more sales is conducted from the office, effectively rendering more and more sales as inside sales.