What is Alpha?

Alpha definition and meaning on Dictionary terms:

the first letter of the Greek alphabet (A, ?).
the vowel sound represented by this letter.
the first; beginning.
(initial capital letter) Astronomy. used to designate the brightest star in a constellation.
Chemistry. one of two or more isomeric compounds.
the first in a series of related items: frequently used in chemistry and physics.
Chiefly British. a mark or grade corresponding to an A.Compare beta(def 8), gamma(def 9).