"sp" just means species. Avicularia sp means "a species of Avicularia". By itself it doesn't mean "unknown" or "undescribed" - but it is a common way of listing an unknown or undescribed species. Sometimes the shorthand "sp" is used when discussing animals where it is not necessary to list the species. For example, if you are discussing Aphonopelmas in general, it's not necessary to list each species of Aphonopelma - easier to just refer to the collectively as Aphonopelma spp.
Thank you for clarifying! I've been wondering about the difference between sp. and spp."sp" just means species. Avicularia sp means "a species of Avicularia". By itself it doesn't mean "unknown" or "undescribed" - but it is a common way of listing an unknown or undescribed species. Sometimes the shorthand "sp" is used when discussing animals where it is not necessary to list the species. For example, if you are discussing Aphonopelmas in general, it's not necessary to list each species of Aphonopelma - easier to just refer to the collectively as Aphonopelma spp.