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.
angle of deviation 1. Angle through which a ray of light is deviated on reflection by a mirror, or refraction by a lens or prism. 2. Angle between the visual axis (or line of sight) of the deviated eye in strabismus and the straight-ahead position while the other eye fixates straight ahead.