In Prolog, dynamic predicates refer to predicates whose definition can be modified or extended dynamically during program execution. Dynamic predicates allow for the dynamic addition and removal of clauses, which can alter the behavior of the program at runtime. Here's an explanation of the concept and when dynamic predicates are useful:

1. Dynamic Predicate Declaration : To define a predicate as dynamic in Prolog, you use the `dynamic/1` directive. It informs the Prolog system that the predicate can be modified dynamically. For example:

   :- dynamic my_predicate/arity.​

2. Modifying Predicate Clauses : With dynamic predicates, you can assert new clauses or retract existing ones at runtime. The `assertz/1` predicate is used to add a new clause to a dynamic predicate, and the `retract/1` predicate is used to remove an existing clause. For example:

   assertz(my_predicate(X)) :- ...  % Add a new clause to my_predicate/1
   retract(my_predicate(X)) :- ... % Remove a clause from my_predicate/1​

3. Runtime Flexibility : Dynamic predicates provide flexibility in modifying program behavior while the program is running. They allow you to adapt and update the knowledge base, extend rules, and handle dynamic data or changing environments. This feature is particularly useful in applications that require runtime customization or adaptability. 4. Database-Like Functionality : Dynamic predicates can be used to emulate a database-like functionality in Prolog. They enable the storage and retrieval of facts and rules at runtime, providing a mechanism to maintain a dynamic knowledge base.

5. Rule-Based Systems and Expert Systems : Dynamic predicates are commonly used in rule-based systems and expert systems. These systems often require the ability to add or remove rules dynamically based on changing conditions or user inputs.

6. Interactive Programming : Dynamic predicates are useful in interactive programming scenarios where predicates can be modified during a session or interaction with the user. This allows for interactive exploration, testing, and experimentation.

7. Metaprogramming : Dynamic predicates are a key ingredient in metaprogramming, where programs can manipulate and generate other programs. They allow for the generation of code, modification of program behavior, and execution control based on runtime conditions.