bubble sheet
A form with many blank circles, ovals, or boxes used to enter a person's answers to multiple choice questions. Also known as an "optical answer sheet." The sheets are designed to be scanned by an optical mark recognition (OMR) machine to save time in evaluating them.
The Scantron Corporation in the United States is a major producer of OMR machines and forms, and operates in 98% of US school districts. Given this prevalence, it has become normal to refer to these forms as a "scantron" in the US.