noun.
The point at which an object is closest to the center of mass of the star it is orbiting.
The Century Dictionary and Cyclopedia
noun.
In the orbit of any heavenly body which moves around another, the point where the former approaches nearest to the primary: usually applied to double stars, but also generally to any satellite.
the GNU version of the Collaborative International Dictionary of English
noun.
That point, in the real or apparent orbit of one star revolving around another, at which the former is nearest to the latter.