I have no idea either
Weak, mixed and strong declensions?
Zwakke, gemengde en sterke werkwoorden.
Ik loop, ik liep, heb gelopen (sterk/strong)
Ik bak, bakte, heb gebakken (gemengt/mixed)
Ik vraag, vroeg, heb gevraagd (gemengt/mixed)
Ik maak, maakte, heb gemaakt (zwak/weak)
Voilà.
You might not have known its terms, but that's what it means here.
In German you also have weak and strong noums(?). But I'd have to look that up, before I do any explanations about it. I know that e.g. "Junge" is a strong noun(?)
Der Junge, des Jungen, dem Jungen, den Jungen.