Which of the following refers to private restrictions placed on property?

A covenant refers to a private restriction placed on property that dictates how the property can be used or what can be built on it. This is typically a part of subdivision agreements or community association rules, where all property owners agree to uphold certain standards or restrictions for the benefit of the entire community. Covenants are legally enforceable and are designed to maintain property values and community aesthetics.

The other terms do not pertain specifically to private restrictions on property in the same way. For instance, estoppel is a legal principle that prevents a person from asserting something contrary to what is implied by a previous action or statement. Lis Pendens refers to a pending lawsuit, which indicates that the title to a property is in question, while a gift deed is a legal document used to transfer property ownership without any expectation of payment. These concepts serve different legal functions and are not primarily concerned with placing restrictions on property use.