A respiratory infection (RI) is an infection of a reptile's airways/lungs, shown by open-mouth breathing, mucus, wheezing or clicking — usually triggered by wrong temperatures or humidity, and needing a vet.
Distinguish it from normal basking gape: an RI involves laboured breathing, bubbles/mucus, or noise. It needs veterinary treatment (often antibiotics) plus fixing the husbandry that caused it — this is triage, not a home cure.