| Raking is a technique used to play two or more notes, usually descending that are on two different strings and using the same finger sweeping upwards. For example, Let's say you are playing the C note on the fifth fret of the G string, your next note is A (7th fret) on the D string. Using your index finger only, you hit the C and than sweep your finger to the D string to play the A note.
That is the jist of raking, it is usually used to play more than two notes and can be done in ascending as well as descending patterns. Another way to rake is more of an effect, take the same two notes in the example above. First rake with your index finger than quickly rake the same two notes with your middle finger in quick succession, it will make for a cool rhythm.
Raking is a technique when used properly will have a desired effect, when used incorrectly, will make your playing sound sloppy.
Raking notes is also a term used to describe a bad technique when used un-intentionally.
hope that makes sense. | 
