Pedal tone is when you keep one voice held on one note, while the other voice has more movement. Keep a droning pedal tone note on the B string, fifth fret, while moving lower voice chromatically up and down. I use a pick for the low voice, and ring finger for the pedal tone, but you can use any finger combination you prefer.
This is a great technique warmup, mostly for left hand, although the right hand part can be tricky too, especially when the spread between strings is wider. Besides being good for technique, you can use it to prepare various pedal steel-ish licks. Charlie McNamara reminded me that you can also find a lot of great Grant Green/Kenny Burrell bluesy jazz lines too.
Any kind of line you want, as long as it's not moving superfast, is in there somewhere. You can play simple pentatonic stuff, get a little more chromatic, bluesy, etc.
A great way to make your line "denser" so that it's less thin. It's effective to throw in this texture once in a while as a contrast if you typically play single-note lines-- textural contrast of this kind can make a long solo sound more interesting.
Here is some additional material from guitar colleague John C. McCain--
These are some chords suggested by the double stops in the exercise. (editor's note: depending on the musical situation, the double stops can imply various chords, or you can just hear the non-pedal tones as tension tones against an E chord, or an A. A lot of pedal steel counterpoint licks use the pedal tone as root or fifth of a chord, with lines below. Steel players often will alternate licks using root on top with fifth-on-top licks, in the same solo or same passage. It's also hot to think of the pedal tone as the 7th of a dominant chord. But all that's another discussion-- perhaps I need to do some more posts on this topic!)
some common harmonic implications (courtesy John C. McCain):
e & d = E7 or Asus
e & c# = AMaj or c#m
e & c - CMaj or am
e & b = E Maj or Em
e & Bb = C7 or Em7b5
e & a = AMaj or am or B7sus
e & g# = EMaj
e & g = em or CMaj
e & f# = D9 or F#7
e & f = FMaj7 or dm9
e & e = EMaj or em or modal anything
e & d# = EMaj7 or B7add11
(John C. McCain can be found on myspace. www.myspace.com/johncmccain