>>> ...larger planets are round, due to their atmosphere
>>
>>That was a careless mistake, and should read: "larger planets are round, due to their gravitation.
>
>And rotating planets are ellipsoids - the faster the more ellipsoid, with a speen limit of making a donuts <bg>.

Right, I forgot about that detail. (The point was, small asteroids, like Phobos and Deimos, can have an irregular shape, because the gravitation won't force them into a sphere/ellipsoid).

Many planets rotate so slowly that they are virtually indistinguishable from a sphere. In the case of the planet Earth, the difference in the two main diameters is about 1/300.

But Jupiter rotates so fast, that the difference is about 1/10 - and quite noticeable in a photograph, for instance.

Some stars are also known to rotate so fast that it almost tears them apart.

BTW, another criterion to distinguish a planet from an asteroid (planetoid) might be, whether it has a companion (moon). But this is about as useless, or more useless, than the other criteria. There are several cases known of even fairly small asteroids that are double, so that doesn't automatically make Pluto a planet (Pluto is known to be a double planet or double asteroid). Also, Venus is almost as big as Earth, and has no companion, at least, none of a significant size.