" Glacial acetic acid is a trivial name for water-free (anhydrous) acetic acid. Similar to the German name Eisessig (ice-vinegar), the name comes from the ice-like crystals that form slightly below room temperature at 16.6 °C (61.9 °F) (the presence of 0.1% water lowers its melting point by 0.2 °C).
A common abbreviation for acetic acid is AcOH, where Ac stands for the acetyl group CH3−C(=O)−. Acetate (CH3COO) is abbreviated AcO. The Ac is not to be confused with the abbreviation for the chemical element actinium. To better reflect its structure, acetic acid is often written as CH3C(O)OH, CH3C(=O)OH, CH3COOH, and CH3CO2H. In the context of acid-base reactions, the abbreviation HAc is sometimes used, where Ac instead stands for acetate. Acetate is the ion resulting from loss of H+ from acetic acid. The name acetate can also refer to a salt containing this anion, or an ester of acetic acid.