"What do the strange words mean?"

Translation: Co znamenají ta zvláštní slova?

[MarimoKun]

"Co ta zvláštní slova znamená" Why not?

[VladaFu]

znamenají is the right plural (3rd person) form

[cwant58]

Would "znamenajou" be a correct conjugation as well?

[AgnusOinas]

Not in standard Czech.

"znamenajou" is a dialectal form in some parts of Moravia, along with "znamenajú" and "znamenajó" in other parts of Moravia, or "znamenaj" in many parts of Bohemia (incl. Prague). So as you can see, the 3rd person plural has a variety of endings depending on the region. But the only standard form here is "znamenají".

https://prirucka.ujc.cas.cz/?slovo=znamenat