Scrum has sprints. Kanban has cards. Shape Up has bets. Every methodology has a "unit of work" — the smallest thing you plan, assign, track, and ship.
For the last 20 years, that unit was the ticket. User story. Task. Issue. Whatever you call it.
In spec-driven development, the unit of work is the spec.
This isn't a rename. The spec behaves differently from a ticket in every way that matters.