Today the word rock has taken on a very general connotation, and is used to refer generically to an enormous amount of subgenres which have ended up branching out and creating more and more confusion. To avoid this ambiguity, some refer to this variety of genres as guitar music, literally “music made with the guitar”, the main instrument of rock.
It seems clear that “rock” music is extremely varied and complicated to frame in a linear path. So let’s try to better understand how rock was born, what its Principal traits are and what subgenres were born during the years thanks to it.
Usually Rock is based on the use of some specific instruments that make its sounds completely different from the other genres, such as the electric guitar. Generally this is accompanied by drums and electric bass, that are essential for the rytmic part of the songs
In the 60’s rock bands usually used other instruments although less frequently. Among these we have the harmonica and the saxophone, generally used for small solo parts.
But let’s go back at the general composition of rock groups all over the years (from 1960 to 2000), they are almost always made up of 4 elements: the drummer, the bassist, the guitarist and the singer. Rarely the bands have 5 or 6 members or it can be formed only by 2 or 3 people. Usually there is no precise outline of the roles as a musician can cover more than one. Generally, the leading role is given to the singer, this because is where the attention of the public goes.
Some people tend to consider rock a continuity of the famous “rock & roll”, but the two genres should not be confused, because they have some different characteristics.
Rock and roll was a genre that came from the union between jazz and country during the fifties.
Only after the first years of the 1960s can we talk about rock in a stricter sense.
The themes covered in rock lyrics include politics, pacifism (a really important theme for America in that period) and in general criticism of the surrounding world and future prospects of life. At the same time, typical elements of youth counterculture enter the lyrics, such as drug use, family conflict and the sexual revolution, in fact how we can imagine this type of music was the way to (especially for the young people) rebel from the authority.
The peak of the golden age of rock arrived with the famous Woodstock Festival, which took place from 15 to 18 August 1969. This festival started a new season of concerts all over America.
So how you could see is quite difficult to define rock , first of all because of all the subgenres that are very similar, but also because maybe a band can be influenced by two or more genres.

Sources
https://www.liveabout.com/what-is-rock-music-2898293