What is the true name for Kyubey?
The name Kyubey is a short-hand for Incubator (pronounced [in-kyuh-bey-ter](source), which shows similar phonetic pronunciations). This follows a pattern similar to other nicknames or names that are shortened, such as:

&quot;Ed&quot;, from &quot;Edward&quot; (e.g. Edward &quot;Ed&quot; Elric from FMA) and
&quot;Al&quot;, from &quot;Alphonse&quot; (like Alphonse &quot;Al&quot; Elric, also from FMA).

That said, Kyubey is the name of the creatures, whereas Incubator is its race/species.
From the Madoka Magica wiki:

Kyubey is an Incubator/Messenger of Magic. Because of this, he, like his race, cannot exhibit emotions of any kind.

In episode 8, around 20:10, Homura says

I won't let things go according to your plans, Kyubey.
Or should I say... &quot;Incubator&quot;?

Which would be equivalent, in context, to me saying

I won't let things go according to your plans, Memor-X.
Or should I say... &quot;Human&quot;?