Basically, a clave is a five stroke pattern used in a tune. Clave is a key element for lots of music cultures now, such as Afro-Cuban jazz, reggae and many more. Clave, in a fancy way, is the structural core of all Afro-Cuban music.
First of all, clave has its root down to tribal African music and believed to be originated in sub-Saharan Africa very early in the music history. However, with the early stages of Latin jazz and other genres in Latin America, Afro-Cuban music embraced the clave theory to their repertoire.
In bold outline, there are two main types of claves which are used mainly in Afro-Cuban music: Son clave, rumba clave.
Son clave, is the most common clave pattern used in Afro-Cuban music. It is traditionally written 2/4 time and are composed of two cells. The rhythms goes like this: ONEtwothree FOUR fivesix SEVENeight | onetwo THREEfour FIVEsixseveneight. The first cell is called the three-side cell, as it contains three strokes, and the subsequent cell is called the two-side cell, as it contains two strokes. In addition, first three strokes of son claves are generally called "tresillo"s.
Rumba clave, is the other clave pattern used in Afro-Cuban music. Rumba form sometimes shows up as 12/8 and sometimes as 4/4 beats, depending on the type of music genre or instruments used in the certain Cuban tune. Unlike the son clave, rumba clave is composed of cell but is classified as 2-3 and 3-2 sequences based on the technique. The only difference that between a 4/4 rumba clave and son clave is that the third stroke in the rumba clave is played one sixteenth note later (Or the first rest is one sixteenth note longer). The other rumba, which 12/8 is used, subdivided into four, three quavers. The rhythms goes like this: ONE two THREE - one two THREE - one TWO three - ONE two three.
Understanding claves is key to understand and analyze any Cuban or Latin music, especially jazz. Although this is only an introduction, it must have given you a slight understanding of the deep clave theory. Stay tuned for more music theory!