WordNet (r) 3.0 (2006):

laptop
    n 1: a portable computer small enough to use in your lap [syn:
         laptop, laptop computer]

The Free On-line Dictionary of Computing (30 December 2018):

portable computer
laptop
laptop computer

    (Commonly, "laptop") A portable personal computer
   you can carry with one hand.  Some laptops run so hot that it
   would be quite uncomforable to actually use them on your lap
   for long.  The term "notebook" is often used to describe
   these, though it also implies a low weight (less than 2kg).  A
   "luggable" is one you could carry in one hand but is so
   heavy you wouldn't want to.  One that can by easily operated
   while held in one hand is a "palmtop".

   The computer considered by most historians to be the first
   true portable computer was the Osborne 1 but see the link
   below for other contenders.

   History of laptop computers
   (http://inventors.about.com/library/inventors/bllaptop.htm).

   (2007-05-21)