Organisms which are polyploid have an extra entire set of chromosomes. For example, humans have 2 sets of 23 chromosomes, for a total of 46. A human that had 3 sets (69) or 4 sets (92) would be polyploid. However, this rarely occurs with vertebrates; most such individuals would not live. It does occur in plants, though, and is hypothesized to be one way new species can arise.