U CAN USE SHOTCUTS WITH IN THE MAPPING WHERE AS REUSABLE 
OBJECTS U CAN USE ACROSS MAPPINGS OF THE EPOSITORY

Hi,  REKHA
Can u check your answer ! Thanks for Posting.

"""  A shortcut is created by assigning 
'Shared' status to a folder within the Repository Manager 
and then dragging 
objects from this folder into another open folder"""""


If any Corrections Let me know
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A shortcut is a reference (link) to an object in a shared
folder these are commonly used for sources and targets that
are to be shared between different environments / or
projects. A shortcut is created by assigning 'Shared' status
to a folder within the Repository Manager and then dragging
objects from this folder into another open folder; this
provides a single point of control / reference for the
object - multiple projects don't all have import sources and
targets into their local folders. A reusable transformaion
is usually something that is kept local to a folder examples
would be the use of a reusable sequence generator for
allocating warehouse Customer Id's which would be useful if
you were loading customer details from multiple source
systems and allocating unique ids to each new source-key.
Many mappings could use the same sequence and the sessions
would all draw from the same continuous pool of sequence
numbers generated.

Shortcut object will be used in across different folder 
where as reusable will be valid in with in folder