Praise be to Allah.
Yes, qaza‘ refers to shaving part of the hair and leaving part of it.
As for cutting part of the hair, for example on the sides, and leaving the top, this does not come under the definition of qaza‘, but if it is cut very short, then it is also disallowed, because it resembles qaza‘.
And because cutting the hair in this manner, nowadays, is one of the characteristics of disbelievers and evildoers; it is not one of the characteristics of people of dignity and good character, so it is not appropriate for the Muslim to resemble those evildoers.
We asked Shaykh ‘Abd ar-Rahmaan al-Barraak (may Allah preserve him) about what is mentioned in the question, and he replied:
This resembles qaza‘ even though it is not qaza‘.
In some cases it is one of the ways of imitating the disbelievers that has been introduced among the Muslims. End quote.
This has been explained in some detail in the answer to question no. 110209.
And Allah knows best.