Again this is my own term and not a universal one. This is the hand position that is most often used to play blues, rock and country lead guitar lines. Because most of the time when you are playing out of a pentatonic scale, you are only going to be playing 2 notes per string. Most of the time in this style of playing, you are mostly using your 1st, 2nd, and 3rd fingers. If you were to use your 4th finger, you would have to move back into the home base position.

For more information on pentatonic scales check out these lessons.

Minor pentatonic - it's the king daddy of all scales used for improvisation on the guitar

All of the basic improvisation lessons deal with pentatonic scales.

For "pentatonic position", you are going to bring your thumb up higher on the back of the neck. Turn your hand to the side, and even rest the outside of your 1st finger on the bottom of the neck.

Pentatonic position is also lends itself well to bends. When you bend a string, you need to have the support of having your thumb up on top of the neck. Bends are very difficult in home base position

Here are a couple of videos to check out of me playing in pentatonic position.

view from above (50K) get realplayer

front view (69K) get realplayer

No matter what position you left hand is in, avoid putting the palm of your hand on the back of the guitar. Your thumb might be wrapped over the top of the neck, but there will still be space between you palm and the back of the neck.

Page 1, Home base left hand position on the guitar

Page 3, Left hand position for chords on the guitar