A Grand Cross is a planetary alignment in the astrology chart. It consists of four planets at 90-degree angles with each other and each being in a different astrological quality.
Every sign of the zodiac is either cardinal, mutable, or fixed. Therefore, a Cardinal Grand Cross happens when all four planets involved are in the cardinal signs of Aries, Cancer, Libra, and Capricorn. This brings a very different energy to the Grand Cross than say a Fixed Grand Cross or a Mutable Grand Cross, for the cardinal energy is probably the most frustrating of the three because of the lack of patience, even though Grand Crosses can be challenging enough in and of themselves.