A slide or slider phone is a mobile phone form factor where the phone is designed like a clamshell phone, in that each half of the phone is dividing the display and speaker from the keyboard buttons. However, rather than the halves being hinged to open and close, the two halves slide open. On a slide phone the main display screen can be viewed when the phone is in the closed position. Examples of slide mobile phones include the Nokia 6600, the T-Mobile Sidekick Slide, and the Samsung D900 Slide Phone.
See also "The Difference Between a Cell Phone, Smartphone and PDA" in the "Did You Know..." section of Webopedia.