The gingival sulcus is an area of potential space between a tooth and the surrounding gingival tissue and is lined by sulcular epithelium. The depth of the sulcus (Latin for groove) is bounded by two entities: apically by the gingival fibers of the connective tissue attachment and coronally by the free gingival margin.
A periodontal pocket is a dental term indicating the presence of an abnormally deepened gingival sulcus.
Rickne C. Scheid (2012). Woelfel's Dental Anatomy. Lippincott Williams & Wilkins. p. 200. ISBN 978-1-60831-746-2.