"An abscess is a localized pocket of pus caused by infection from bacteria. More common in Crohn’s than in colitis, an abscess may form in the intestinal wall—sometimes causing it to bulge out. Visible abscesses, such as those around the anus, look like boils and treatment often involves lancing. Symptoms of an abscess include swelling, tenderness, pain, and fever. Once the abscess is drained, the symptoms resolve. Antibiotics are usually given to clear up the remaining infection."

References:

1. https://www.crohnscolitisfoundation.org/sites/default/files/legacy/assets/pdfs/intestinalcomps.pdf