Spine tilt is simply the angle of your spine at address. When you bend over to reach the ball, you tilt your spine and it forms an angle with the ground. When you swing, it's important to maintain that angle all the way back and all the way through impact. If you decrease your spine angle,stand up, you will raise your shoulders and arms, causing you to hit the ball thin. If you increase your spine angle, bend over more, you will lower your shoulders and arms, causing you to hit the ball fat. Solid, consistant ball contact can only occur when your spine angle is the same at impact as it was at address. Try to maintain a straight spine and rotate around your spine. Try to finish your swing with your spine at the same angle as it was at address. This will help keep your head still over the ball. I hope this answers your question for you on spine tilt angle. Didn't want you to have to wait until on of the site pros gets a chance to reply.

Some good observations, Don. Spine angle "issues" (changing the angle of the spine during the swing) are generally caused by one of two things or a combination of the two. First of all, people who slouch too much at address (too much curvature in the spine) are often here and there and everywhere in their swing. Lots of motion, lots of lifting, etc. Stems from poor posture at the start. Secondly, a swing plane that is "off" can be the root of spine angle issues. Generally, people who swing on too steep a plane will come up and out of a shot (raise spine angle) to avoid the pain and hurt involved in hitting the ball fat. It's a "compensation" move. Thus, it's not effective "trying" to not do that. The issue, in that case (and it's an exceedingly common one, I might add), has to be tackled at the source. Make sense?
Andrew