Is an abnormal growth on the body considered a cyst?

It depends on the structure and the appearance of the
growth.

For example, a cyst is a benign tumor, whose aspect
is like a closed bag, filled with a liquid or semi-liquid content. The content of the
cyst is limited by an own wall. All organs may contain cysts. They can disrupt the
functioning of an organ , compressing it, or they may cause aesthetic damages.
Generally, they are treated either by needle puncture or by surgical
removal.

Also, the abnormal growth could be a nodule.
Nodule is a small bulge, well circumscribed, which is occurring in various parts of the
body, some chronic diseases being oftenly accompanied by a
nodule.