A home button on a smartphone, tablet or other electronic device that is an icon on the touchscreen.  Tapping the home button displays the start screen.  Contrast with a "physical home button," which is hardware and must be depressed.  See 
home button.
Physical and Virtual
An iPhone has a physical home button but can also display a series of virtual buttons as one of its accessibility functions.  These six white icons are displayed by tapping a single button that always remains on screen when the virtual feature is activated.