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.
Quartile Deviation (QD). The quartile deviation is half the difference between the upper and lower quartiles in a distribution. It is a measure of the spread through the middle half of a distribution.