Final answer:
A restrictive covenant is a provision in a deed that limits the use of the property and prohibits certain activities. In this case, the clause preventing X from putting a fence around his front yard would be considered a restrictive covenant.
Step-by-step explanation:
Restrictive covenants are provisions in a deed that limit the use of the property and prohibit certain uses. In the given scenario, the clause in the deed that states X is not allowed to put a fence around his front yard would be referred to as a restrictive covenant. This type of covenant is used to establish specific rules and restrictions for the property, often to enhance the neighborhood and maintain a certain aesthetic.