Dogfooding means a startup uses its own product to run its own business. Dropbox stores its own files, Slack runs its own internal communication, GitHub builds GitHub on GitHub. The discipline forces the team to feel every rough edge and prioritize fixes the way customers would.
The practice has limits: internal users are a self-selecting power-user segment and won't surface every edge case. Dogfooding should complement, not replace, customer research and bug reports from real cohorts.