[amsat-bb] G3RUH plan 13 algorithm help

[Lizeth Norman]

*HI all,Found this at this
page:http://www.amsat.org/amsat/articles/g3ruh/111.html
<http://www.amsat.org/amsat/articles/g3ruh/111.html>Orbit Plane:* Fixed
(almost) with respect to the stars, in orientation defined by argument of
perigee, inclination and RAAN.
Origin: Earth's centre.
X: Directed towards perigee
Y: 90 degrees from perigee round the orbit in direction of satellite's
motion
Z: Perpendicular to orbit plane
I think I understand most of the math in the algorithm. In the above
context, what does RAAN mean?
Sorry for being obtuse!
Norm n3ykf