Cooperman, I'll take a try. The blues is a musical form. There are variations of it.
The traditional twelve bar blues has three lines. You state the first line and then repeat it the second time while you are trying to think of the way to rhyme and end it on the third.
The harmonies have changed over the years to accommodate the growth of jazz. One could argue that Charlie Parker was one of the greatest blues musicians that ever lived.

The blues singer emanates from the African-American tradition of outdoor slave hollers
and farmers. It has gone through a metamorphosis of a rural expression to the night clubs of Chicago and through the propagation of what was called "Race Records" by independent recording companies targeting Black audiences. The thematic material centers around hard living conditions and dysfunctional love lives.

There are few optimistic blues but there was
a genre called the "Party Blues" which was used to dance to and the verses were often risque.

The Cabaret Blues of the whorehouses in New Orleans were basically composed songs by the musicians that accompanied the Blues Chanteuse singers such as Bessie Smith. Some of the songs called blues by them were really out of the traditional 12, 8 bar or 16 bar forms. They were more like popular songs. The singers, however, retained a blues shouting style.

Most of the early rock and roll influences came from blues musicians in the clubs who played electric guitars for dancing. Some of the rural blues singers such as McKinley Morganfield moved to the big city (Chicago) and became Muddy Waters. Big Bill Broonzy started as a fiddler playing the blues in Georgia and moved to Chicago where he took up the guitar to accompany his singing.

When Black musicians took over the blues forms and changed them, the music became
broadened and included a popular base. Louis Armstrong, Charlie Parker, were two outstanding musicians who played the blues.

There is a question whether the Piedmont style of guitar playing which had a ragtime feel could be called the blues. The same problem is presented in analyzing the music of Leadbelly although he played the De Kalb Blues and the Red Cross Blues. Josh White popularized (some say watered-down) the blues by bringing into the Cafe Society crowd in New York. Billie Holiday was often referred to as a blues singer but very few of the songs she recorded were actually blues.

There is a substantial blues tradition. Like folk music, it is a flowing river that has many tributaries but it keeps on nourishing those who are into it.