To "imply" means to suggest without actually saying it directly.
For example, someone may look at their watch when you are talking to them. This implies that they are in a hurry without actually saying it out loud.
If you implied criticism you would say something in a vague, casual way.
If someone said a woman's dress was too tight, it MIGHT be an implied criticism. They haven't said she is fat but they seemed to imply it.
However, sometimes people think there is an implied criticism when there is none!
What was said might not have been DELIBERATE, just a bad choice of words or actions.
Hope this helps