What is the meaning of post-op transsexual?

A post-op transsexual refers to a person born with transsexualism who had their condition corrected with surgery. So the transsexual woman is just a woman afterwards. Likewise, the TS man is just a man.

A pre-op TS is a person who was born with transsexualism (who is not merely transgendered) who will someday get the surgery.

There is also a non-op TG who people often mistakenly call a non-op TS. That is a man who lives as a woman, or a woman who lives as a man, and who intends on never getting surgery. They are likely not transsexual at all. That is not the same as a pre-op TS who is living in poverty or who is in bad health. The fact they would get surgery if they could would make such persons pre-ops.