Referent is data that reference refers to 
Use ref function to determine referent type 

scalar value: '' 
reference to scalar value: 'SCALAR'
array reference: 'ARRAY'
hash reference: 'HASH'
code reference: 'CODE'
reference to typeglob: 'GLOB'
reference to precompiled regexp: is not available in 5.004 which is installed here
reference to a reference: 'REF'
reference to an object: 'Point'