Final answer:
In ServiceNow, the 'clone_target' property must be set to true for an instance to be a clone target, which allows for data replication in cloning operations.
Step-by-step explanation:
The glide property that must be set to true to allow an instance to be a clone target in the context of a ServiceNow instance is the clone_target property. When this property is enabled, the ServiceNow instance can be selected as a destination for cloning operations, meaning that data from another instance can be replicated onto it. This is particularly useful in situations where you want to create test environments that mirror the production environment without affecting the live system.