can·cel·la·tion / ˌkansəˈlāshən/ • n. the action of canceling something that has been arranged or planned: train services are subject to cancellation at short notice. ∎  a crossing out of something written. ∎  a visible or electronic mark placed on a postage stamp to show that it has been used. ∎  Law the annulling of a legal document.

cancellation The loss of significant digits in subtracting two approximately equal numbers. This is a frequent cause of poor accuracy in numerical results but it can usually be avoided by some reorganization of the calculation. Consider, for example, the quadratic equation ax² + bx + c = 0

The formula for the roots of a quadratic is (–b ± √(b² – 4ac))/2a

If b² is large compared with 4|ac| severe cancellation occurs in one of the roots. This root can be computed from the fact that the product of the roots is c/a.