Final answer:
The term for a crackling breath sound indicating fluid in the lungs is 'crackles'. It is a sign that may point to conditions like pneumonia or heart failure.
Step-by-step explanation:
The crackling, rattling breath sound that signals fluid in the air spaces of the lungs is described by the term crackles. These sounds are indicative of a variety of respiratory conditions where fluid accumulates in the air sacs, commonly occurring with pneumonia, heart failure, and other pulmonary ailments.
It is vital for healthcare providers to recognize these sounds, as they may signify the need for prompt medical attention.