A carrier lock is a restriction imposed by a mobile network operator on a mobile device, such as a smartphone, that prevents the device from being used with other networks. This lock is typically implemented through software or hardware and can be either permanent or temporary.
There are several reasons why a carrier might lock a device. One reason is to encourage customers to stay with their network by making it difficult or impossible to use the device with another carrier. Another reason is to recoup the cost of subsidizing the device. When a carrier offers a device at a discounted price, it often requires the customer to sign a contract agreeing to use the device with that carrier for a certain period of time. If the customer breaks the contract, they may have to pay a fee to unlock the device.