Polyploidy = cells that have more than 2 homologous sets of chromosomes (humans are polyploidy because we have 2 sets; this is known as diploid)
Euploidy = cell has an integral multiple of the monoploid number (with possible exceptions including sex chromosomes). For example, humans have 46 chromosomes (2 x 23). Aneuploidy (which is the opposite of euploidy) would be like having 47 chromosomes.
These terms (polyploidy vs euploidy) are not mutually exclusive.
