The notice period (Kündigungsfrist) is how long you need to cancel a contract, fire an employee, or quit your job.
All jobs have a notice period, both for the employee (when they quit) and the employer (when they fire someone).1 It depends on your work contract, and how long you work at that company.
Apartment leases usually have a 3-month notice period. It starts when the landlord receives your cancellation letter. You must pay rent until the end of the notice period.
How apartment notice periods work
Many other contracts have a notice period. In some cases, you can cancel a contract early if there is a price increase, you leave Germany, or you move where the service is not available.2 This is called a Sonderkündigung.