It associates those people born "under" one of these with c…

They were called moveable by traditional astrologers because, as Bonatti says, the "air" changes when the Sun enters each of these signs, bringing a change of season.

Angular signs are those signs which are located on the astrological angles of any given natal chart. Angular houses may be cardinal, fixed or mutable, depending on the birth time of the chart but only Aries, Cancer, Libra, and Capricorn are cardinal signs.

Their starts are related to equinoxes and solstices.