To press a physical button or tap a virtual button on a touchscreen and hold it down for a second or two. Employed on touchscreens, smartphones, tablets and smartwatches, the long press or long tap increases the flexibility of the user interface. The normal "short press" or "short tap" (releasing right away) performs one operation, while pressing/tapping and holding that same button for a short time activates another. For example, a short press of the iPhone's home button retrieves the home screen, while a long press launches the Siri virtual assistant.
You May Have to Release
Some functions activate while you keep pressing. For example, pressing the home button on an iPhone or iPad and not letting go will cause Siri to ask you what you want. In contrast, tapping an icon in the list on the left side of the Windows 10 Start menu will cause nothing to happen until you let go.
Long Press/Long Tap Vs. Force Touch/3D Touch
Apple's Force Touch and 3D Touch sense the actual pressure applied. However, a long press or long tap are time based and can be implemented in most any application. See Force Touch
and drag and drop