Definition and Usage

The multiple attribute   of select tag is a boolean attribute which allows the user to select more than one option  can be selected at a time. Browsers typically present multiple select lists in a different way to a normal select list.

If the  multiple attribute isn’t present in the control, only one option in the list can have the attribute selected declared.

To select more than one option in a multiple selection list, users can click options while holding down the CTRL key. A range can also be selected using the SHIFT key.