What is the difference between anti-aromatic and non aromatic compounds?

The reactivity and geometry of the compound

What characterizes an aromatic compound it's cyclic, planar, and have a conjugated system of p orbitals perpendicular to the plane of the molecule, and this conjugation makes the molecule very stable.

So a non aromatic compound is either not cyclic or not planar. And an anti aromatic compound is cyclic, planar and has the conjugation of p orbitals, but the difference is the number of electrons in the conjugated p orbitals.

While aromatic compounds follows Hückels rule and has 4n + 2 electrons conjugated we can say the orbitals are 'full', an anti aromatic compound just have 4n electrons conjugated so the molecule is very reactive.