The three terms used to compare a cell's osmolarity with its surroundings are hypotonic, hypertonic and:

1. The comparison has three possible outcomes: outside lower, outside higher, or the two equal. 2. Hypotonic covers lower and hypertonic covers higher. 3. Three terms, hypotonic, isotonic and hypertonic, are used to relate the osmolarity of a cell to that of the extracellular fluid. 4. So the equal case is isotonic. _Source: OpenStax Biology for AP(R) Courses (CC BY 4.0), Ch 5 'Structure and Function of Plasma Membranes', sections 5.1-5.4_