Simple Definition:

Hydrolysis is a chemical reaction [a process where substances combine or break apart] that uses water to break down [split] a compound [a substance made of atoms from different elements] into simpler molecules. This reaction occurs when water molecules interact with the chemical bonds [connections between atoms] in the compound, resulting in the formation of new substances.

For example, when water reacts with a salt like sodium chloride (NaCl), hydrolysis occurs, breaking the salt into sodium ions (Na+) and chloride ions (Cl-).

Very Simple Definition:

Hydrolysis is a process where water helps to break things into smaller pieces.

For example, when you put a lollipop into your mouth, your saliva (which contains water) starts to break down the sugar in the lollipop, making it taste sweeter.