"serial monogamy, marriage with only one other person at a time, in contrast to bigamy or polygamy[.] Some definitions of serial monogamy consider it to be polygamy, as it can result in evidence of genetic polygamy. It can also be considered polygamy for anthropological reasons."

So, "serial monogamy" vs "serial polygamy" seem to be two different interpretations of the same phenomenon:

- Serial monogamy: multiple monogamous relationships

- Serial polygamy: a polygamous relationship where the individual partners/relationships are separated in the time domain (like time-division multiplexing (TDM) in engineering: https://en.wikipedia.org/w/index.php?title=Time-division_mul...).