what is a neoplasm cyst?

Answer 1

Breaking it down into its terms....

Neoplasm- Mass of abnormal cells (normally stemming from one changed cell), that are grown more than they should have done. Possibly have lost contact inhibition (where a cell touching the basement membrane should not proliferate).

Cyst- A fluid filled mass.

So basically it is a bunch of abnormal cells surrounding a fluid filled centre. There are a lot of other factors surrounding what you have asked. A neoplasm is term that can describe many abnormal cells and its specific meaning depends on specific cases.