Sinusitis refers to the inflammation of the sinus cavities, which are located around the nasal area. It can occur due to infections (viral, bacterial, or fungal), allergies, nasal polyps, or other factors that obstruct sinus drainage. Symptoms of sinusitis include facial pain, nasal congestion, thick nasal discharge, headache, and reduced sense of smell. Treatment may involve medications such as pain relievers, decongestants, nasal saline irrigation, or antibiotics if a bacterial infection is present.