The changes in chromosome number by additions or deletions of less than a whole set is aneuploidy. In this case organism gains or loses one or more chromosome but not a complete set. Polyploid is defined as the addition of entire set of chromosome. The polyploidy can be tryploidy $(3 n)$ tetraploidy $(4 n)$, pentaploidy $(5 n)$ etc.
Allopolyploidy is the polyploidy in which chromosome sets are non-homologous. Monosomy is the process in which one chromosome is removed from dipoid set of chromosome $(2 n-$ 1).