Slash Chords are chords where the bassnote changes. You may have seen something like this: C   C/b  Am    For this example you play a chord of C for one bar, then lower the C bassnote to a B while keeping the rest of the previous C chord in your fingers. For the last chord you play a Am.  If you obseve the movement of the bassnotes you will notice they fall down step by step, they form a little melody or movement on their own.

Slash chords are great for adding some spice to your chords.
The opposite of using Slash chords is using pedal notes: Keep one note (bassnote) the same while you change the rest of the chord. Take this idea a bit further and you get to drones: One note (or a few) which serve as harmony for the rest of your melody (or improvisation). Drones are used often in Indian Music. Some African music also uses this kind of idea.

Happy Playing
Eddie