The checkbox is an <input> element that can be selected or deselected by the user. Only the selected checkboxes are included in the submitted by the browser. The submitted checkboxes follow the standard syntax name1=value1 & name2=value2

name1 - the value of the name attribute of the checkbox <input> element and
value1 - the value of the value attribute of the same checkbox <input> element.
To insert a checkbox, use the <input> element with the type attribute set to "checkbox". There is another attribute that can be used in conjunction with the checkbox element.
checked for when the default state of the checkbox element is selected

It is possible to have more than one checkbox with the same name. All these elements are submitted if the user selects them.
If the value attribute is not included, only the selected checkboxes will be submitted to the receiver, using a syntax like: "checkbox_name=on". It is recommended that you avoid this situation.
Related Tutorial
11. checkbox