In another book Al-Jabr wa-al-Muqabilah (Book of Calculations, restoration and reduction) is where the word algebra (Al Jabr in Arabic) was first used. Al-Khorezmi was also the first scientist to define and represent algebra as a science. In his work he submitted six canonical types of linear and square equations and basic methods of solving them, methods which are still used.
The word "algebra" was latinised from the Arabic word "al-jabr", which is evident from the Arabic title of the treatise. The word stands for "filling in" - one of the fundamental operations in algebra at that time.
These works tremendously influenced the development of Science in both the Muslim World and in Europe making him one of the most important mathematician, astronomer and geographer of his age.
Source: Wikipedia http://en.wikipedia.org/wiki/Mu%E1%B8%A5ammad_ibn_M%C5%ABs%C4%81_al-Khw%C4%81rizm%C4%AB and www.orexca.com/p_khorezmiy.shtml