A mobile operating system originally developed by Palm and later acquired by HP in 2010. webOS was initially used as a replacement for Palm's earlier Palm OS mobile operating system as well as Microsoft's Windows Mobile, which the company used on some of its smartphones. webOS powered a number of Palm and HP smartphones before being expanded to also run on tablet computers like the HP Touchpad.
In 2011 HP announced its intentions to develop a version of webOS that would run within Microsoft Windows operating systems and that would be installed on all HP desktop and notebook computers. However, by August of the same year HP declared it was ceasing development on webOS and that future webOS-powered devices would be discontinued as well.
See Mobile Operating Systems (Mobile OS) Explained in the Did You know...? section of Webopedia.