A small, soft, red-to-yellow nodule ('gum boil') on the attached gingiva that intermittently drains pus is most likely a:

A parulis is the soft-tissue opening of a draining sinus tract from a chronic periapical or periodontal abscess. Trace the tract (often with a gutta-percha cone and a radiograph) to find the source tooth; treatment targets the underlying infection (endodontic or periodontal).Other options: A fibroma is firm and non-draining; a torus is bony and hard; an amalgam tattoo is a flat gray-blue pigmentation.Key exam takeaway: A draining 'gum boil' is a parulis; locate the source with a gutta-percha tracing radiograph and treat the cause.