Incertae sedis

Incertae sedis means "of uncertain position". It's used when scientists aren't sure which category an organism belongs to. For example, let's say you're a scientist studying a type of crab that you've never seen before. You might need to do some research to figure out which category the crab belongs to. If you don't know where to put it, you would say that it is incertae sedis, meaning of uncertain position.