Here, by default both apt-cache and aptitude search for a package on whole list of packages in repository, but output of aptitude shows whether the package is installed on the system or not by giving a per-package flag which here is 'p' indicating that package is present but not installed and 'i' which indicates that the package is installed, whereas apt-cache just lists the package and its one-line detail without telling if package is installed or not.
deviation deÂ·viÂ·aÂ·tion (dÄ'vÄ-Ä'shÉn) n. A turning away or aside from a normal course. An abnormality. Deviant behavior or attitudes. The difference, especially the absolute difference, between one number in a set and the mean of the set.
deviation. 1  the act of deviating. 2  departure from a standard or norm. 3  Statistics. the difference between one of a set of values and some fixed value, usually the mean of the set. 4  Navigation. the error of a magnetic compass, as that of a ship, on a given heading as a result of local magnetism. 5  Optics.