Short[expr] prints as a short form of expr, less than about one line long.
Short[expr, n] prints as a form of expr about n lines long.
Short[expr] gives a "skeleton form" of expr, with omitted sequences of k elements indicated by k.
In StandardForm, the characters used for this output are \[LeftSkeleton] and \[RightSkeleton].
Omitted sequences of elements are printed as Skeleton objects.
Short prints long strings in skeleton form.
The number of lines specified need not be an integer.
Short can be used with InputForm and other formats as well as OutputForm.
Short acts as a "wrapper", which affects printing, but not evaluation.
Trying to feed k as obtained from Short back as input to Mathematica in StandardForm will generate an error.
Short is used to limit the length of output in standard Mathematica warning and other messages.
See The Mathematica Book: Section 1.4.8 and Section 2.8.5.
See also: Shallow, Format.