Checkbox are very common in webpage forms and is used where one more than one option is to be selected out of a given choice by visitors.
Radio button or Checkbox
The difference in check box and period button is the user can't select more than one option in case of period buttons. In checkbox the user can give more than one option. For example in a newsletter script you can ask the visitor to select their interested areas. Here the user can give one or more than one option as the area of interest. So all options are to be stored or covered for the user. This way we can get more than one option for a choice.
In a radio ( or period ) button, we can select one option out of several choices given to the user. In a check box we can select more than one.
More on JavaScript form Validation