An essential element of playing music is being aware of “where” you’re playing in the beat and how it relates to the groove being laid down by the rhythm section. This concept can be broken up into three approaches: playing behind the beat, playing ahead of the beat or playing squarely on the beat.
How a guitar player chooses to interact with the beat, or pulse, will have everything to do with the feeling of the music and the expression being communicated to the listener. This is, of course, true for all instrumentalists, regardless of musical style.