Generally speaking: chemical reaction that takes place when water (solvent) splits molecules into several parts. Hydrolysis reactions involve interactions between ions and water, and they may occur in different ways. Some of them are spontaneous, others require a catalyst (often an acid or a base).

In other words: hydrolysis occurs when polymers break down into monomers thanks to the action of water.

Hydrolysis can somehow be considered the opposite of condensation. Condensation phenomena lead to the formation of bonds between molecules as the water dries. In hydrolysis phenomena water plays, instead, an important role on in breaking the bonds.

In Ceramics, these phenomena may sometimes be very critical.