A Separation

1. The act of disuniting two or more things, or the condition of being separated.

Synonyms: A Detachment, disjunction, A Division, A Rupture, A Severance

Antonyms: An Annexation, A Combination, An Unification

4. The act or condition of two or more people being separated from one another.
5. The act or condition of a married couple living in separate homes while remaining legally married.
   1. (law) An agreement legalizing such an arrangement. Synonym: divorce from bed and board
6. The place at which a division occurs. Synonyms: A Border, A Boundary, A Demarcation
7. An interval, gap or space that separates things or people. Synonyms: A Break, An Interstice
8. An object that separates two spaces. Synonyms: A Barrier, A Separator
9. (military) Departure from active duty, while not necessarily leaving the service entirely.

Astrophysics:

Angular Separation

Linear Separation