Target correction question

My correction target told me I was "thumbing". What exactly does that mean? Also what is the difference between "pushing" and "heeling"? Thank you!
Just so there's no confusion here's the print I used for the target. http://img.tapatalk.com/473c3fc6-5fde-15e5.jpg

Heres a link that gives a brief description for shooting errors that might help a little: http://www.targetshooting.ca/docs/Pi...t_Analysis.pdf

It describes thumbing as "applying too much or inconsistent pressure with the thumb."