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.
In mathematics and statistics, deviation is a measure of difference between the observed value of a variable and some other value, often that variable's mean.tatistics of the distribution of deviations are used as measures of statistical dispersion. 1  Standard deviation is the frequently used measure of dispersion: it uses squared deviations, and has desirable properties, but is not robust.