Ablation is defined as:

1) A surgical excision or amputation of a body part or tissue¹.

2) Removal of an object's surface material by vaporization, chipping, or erosion².

In LASIK, ablation also refers to the smoothness of an incision or alteration. Smoother ablations in this case tend to promote faster healing and better overall vision³.

edit Sources

1) Answers.com

2) Wikipedia.com

3) MPOMG.com