What is the clinical term for the bloody fluid the physician drained

Is there a story behind this question? I think there's more to it, there are several terms used in different situations.

This questions if for Case Study 1 for AMU SCIN 360, here are the rest of the questions, still looking for the answers.
1.   What is the normal fluid in the knee joint?
The knee joint is surrounded by synovium which produces synovial fluid.
2.  What is the clinical term for the bloody fluid the physician drained?
3.  How did this fluid form?
4.  Which signs of inflammation is Stacey clearly showing?
5.  When the physician gives the “injection to reduce the inflammation,” what is likely in the injection?
6.  If the surgeon prescribes a nonselective COX inhibitor for the pain, how does it work?
7.  How is a selective COX-2 inhibitor different from a nonselective COX inhibitor?