I guess due to post appendectomy complications, your incision/wound wasn't close completely or was reopened.
Acctually, if the infection and inflammation in appendix was so severe (your appendix was ruptured) the surgeon didn't close the incision at the end of the surgery because of concern that the wound is already infected.
The gap of the wound is left for drainage of pus.
Also, an abscess can be formed as a complication after the surgery, and the site must be reopened to allow the wound to drain.
If the drainage increases overtime and changes its color, you should contact your surgeon immediately.
Redness, feeling of temperature, are alarming signs.
Best wishes!
Marija