Final answer:
The correct term for the space between the free gingiva and the tooth that rarely exceeds 2-3 mm in depth is a healthy 'gingival sulcus'. It is crucial for oral health to keep this space shallow to prevent periodontal diseases.
Step-by-step explanation:
A healthy gingival sulcus, which is the space between the free gingiva and the tooth, rarely exceeds 2-3 mm in depth. The gingival sulcus is an important area to monitor for maintaining oral health, as deeper spaces can indicate the presence of periodontal pockets, a sign of periodontal disease. Good oral hygiene can help maintain a healthy gingival sulcus and prevent the progression of gum disease.