Definition - What does Slide Phone mean?
A slide phone is a physical mobile phone design in which one section of the phone is used for the display, which slides apart from the other section, which is the keypad.
The key advantage of a slide phone is its ability to accommodate a large screen size and large keypad area without consuming too much outside phone space, particularly when a phone is in a retracted state. When retracted, the keypad remains hidden behind the display area. A user simply slides out the keypad as required. Some keypads slide along the phone's vertical axis, while others slide along the horizontal axis. The keypad has either a standard or QWERTY layout.
Techopedia explains Slide Phone
Phones designed with a touch screen display and keypad benefit from a slide form because designers can make the touch screen interface larger than phones with screens and keypads located on a phone's exterior. For example, the Nokia N97 has a full touch screen display. The keypad slides from underneath the phone, but there is also a full QWERTY keyboard. Without slide form adoption, the N97 would require a relatively wide surface area.
Because accelerometers automatically rotate screen layout between portrait and landscape mode, it is now easier to design phones with keypads that slide from the side of a phone, like the Nokia N97.