What ARE birds?

i'm think gonna give it to CSJ because birds are supposed to be 'animals with eggs that don't lay eggs'. i think i was being too specific about how i interpreted the word viviparous to specifically be with a placenta or something like it, whereas ovovivparity would refer to something that releases live young but basically just hatched eggs inside itself or what have you rather than directly nourishing it. but uh, i think viviparity can be used to refer to producing live young in general as well?

i also dunno if it's fair of me to expect you guys to be more specific than that, especially because i feel like we're gonna go in a circle. that, and i think i've ruled out something someone said when they probably thought it referred to the thing i meant in the first place. @__@