Plain English Meaning
In certain airspace, ATC is actively keeping every aircraft apart by tracking them and giving instructions, rather than leaving it to pilots to see and avoid each other.
Full Definition
The separation of all air traffic within designated airspace by air traffic control, where each aircraft's position, altitude, and heading are actively known, monitored, and directed.
Context Anchor
Seen in air traffic control and airspace discussions, especially when describing areas where controller-provided separation applies to all aircraft.
Derivation
From Latin 'positivus,' meaning 'settled' or 'firmly established.' Here 'positive' means definite and active — control is actually being exercised, not assumed. It contrasts with airspace where separation depends on pilots looking the window.