Definition
A method of separating aircraft by keeping them on different flight paths or in different geographical locations, so that their routes do not converge to the same point at the same time.
Plain English
Keeping aircraft apart side-to-side, by routing them along different paths or through different airspace, rather than spacing them by altitude or by distance along the same path.
Context Anchor
You will see this term in air traffic control, IFR routing, radar service, and separation-minimum discussions.
Derivation
From Latin lateralis, meaning 'of the side.' In aviation it means aircraft are kept apart sideways — on routes that lie to the side of one another — rather than above/below or ahead/behind.
Why Pilots Care
Prevents collisions when aircraft fly parallel or diverging paths in the same airspace.
Intuition Check
Do not read lateral separation as any kind of spacing. It specifically means side-to-side spacing, not vertical spacing or nose-to-tail spacing.
Example Sentence 1
ATC provided lateral separation by routing the two aircraft along parallel airways twenty miles apart.
Example Sentence 2
In nonradar environments, lateral separation is achieved through 15-degree track divergence within 15 minutes of departure.