Also known as: エムエスエックス
Gundam Mobile Suit X, or MS-X (エムエスエックス Emuesuekkusu) for short, is a 1984 series of new Mecha designs and variations of official Mobile Suit designs from the Mobile Suit Gundam animated series.
Just like the Gundam MSV Mobile Suit Variation (MSV) series of designs, these other mobile suit variations are all legitimate canon and were part of an original design series.