If I'm not mistaken, I believe it's when they put the chemo drugs right into the abdomen. My sister has primary peritoneal carcinoma and she had two ports, one by her heart and one on her ribs (lower portion of her ribs). The lower one was to allow the chemo drugs to go into her abdomen.
Please feel free to email me if you have any other questions and I can ask my sister. Hopefully, I'm right in my assumption.