Atelectasis is partial or complete collapse of the lung. Most of the time it is partial, and the radiology report will say something like subsegmental atelectasis. Complete lobar collapse is more serious, and warrants additional workup such as bronchoscopy to rule out an obstructing process, such as mucus plugging or tumor.
Fibrosis is a form of interstitial lung disease that causes scarring and changes the ability of the lung to function normally. As this progresses, this can cause honeycombing pattern as well as adjacent traction bronchiectasis.