What is "groove" music?

A groove is simply a rhythmic pattern, often 2 or 4 bars that repeats itself over and over.  Far from being confining or overly simplistic sounding, the layers and syncopation create a feel that is ideal for dancing and moving one's body to.

Groove tunes are not necessarily limited to one chord: however, in general, the rhythmic concept needs to be repetitive and varying degrees of simplicity often work best. -- John Coltrane's recording of "My Favorite Things" is a good example.  Note McCoy Tyner's hypnotic chord comping, Steve Davis's repetitious bass pulse, and Elvin Jone's unique "layer of sound" style that glues it together, creating a back drop for the soloists' venturous improvisation, yet a solid groove, nonetheless.  --The space that players have to digress from specific comping patterns and branch out without leaving the groove is called the "pocket" and in the recordings of John Coltrane we hear it being stretched in ways that had never been done before, yet is never digressed.

It was James Brown, influenced in part by the Gospel and Soul Jazz of the era, who took this style to its extreme by creating "looped" like musical in which the tunes often stayed on a single chord, but were heavily layered.  --The basic concept of the music is that the entire band, straight down to the horns, guitars and vocalist act as a rhythm section -- not merely the drummer. --His landmark 1967 recording "Cold Sweat", partly inspired by Miles Davis's "So What" marked the beginning of funk as a distinct musical style all to its own.

listening tip:
When listening to groove oriented music, the best way to appreciate it is to take the tune in as a whole, then try to focus in on different parts and notice how they are blending together to create a type of rhythmic and harmonic gestalt in which the sum of the whole seems greater than its parts.   --When creating this type of music, always consider the way simplistic rhythms can be counter laid so that two different things is happening at once, yet they are effortlessly complementing each other without stepping on each other's space.