A more thorough explanation:

Definition: A demand for money, property, or a legal remedy to which one asserts a right, especially the part of a complaint in a civil action specifying what relief the plaintiff asks for. It refers to a claim for an amount previously agreed on by the parties or that can be precisely determined by operation of law or by the terms of the parties' agreement. It can also be a claim that was determined in a judicial proceeding.

Examples:

• A person sues their landlord for not returning their security deposit, which was agreed to be $500 in the lease agreement. This is a liquidated demand because the amount is previously agreed on by the parties.
• A person sues their former employer for unpaid wages, and the court has already determined that the employer owes them $10,000. This is also a liquidated demand because the amount was determined in a judicial proceeding.

The examples illustrate that a liquidated demand refers to a claim for a specific amount that is either agreed upon by the parties or determined by a court. It is different from an unliquidated claim, where the amount owed has not been determined yet.