In mobile computing, multi-touch refers to the capability of a touchscreen (or a touchpad) to recognize two or more points of contact on the surface concurrently. The constant tracking of the multiple points allows the mobile phone interface to recognize gestures, which enable advanced functionality such as pinch-to-zoom.
The multi-touch sensing doesn't work on the resistive type of touchscreens (budget touch phones), the capability comes inherited in capacitive touchscreens (majority of touch phones nowadays).
Apple is considered the pioneer of multi-touch technology on mobile phones with their first iPhone. They introduced the pinch-to-zoom and rotate gestures that are now available across various platforms.