When this box is checked, tapping your finger on the TouchPad surface performs the same action as clicking the primary mouse or TouchPad button. A tap should be a quick down-up motion. It is not necessary to press down firmly.
When the Tap to Click box is unchecked, you must press the actual TouchPad buttons to produce clicks.
If you have a supported pointing stick and it is selected, “Tap To Click” will be changed to “Press-To-Select” and will control the Press To Select feature of the pointing stick.