[It's pronounced more like "grap" (grapple) + "pearl", please don't ask me why they're named that, I don't know.]

Grapearls are manmade gunmen; we created them to improve on the designs of Gurren Lagann and mass produce them, though they do have quite a few flaws that will need to be improved going forward.

[...]

Our gunmen - with Gurren Lagann being our most powerful - are a bit like you. They're very large machines that we can pilot, though they are incapable of speech or thought.

[Just in case you have a very different concept of gunmen!!!]