Occasionalism, interactionism, and parallelism are all schools of philosophical thought regarding mind-body interaction and causality.
Occasionalism is the theory that says substances that are created cannot be efficient causes of events. The efficient cause of an object is that which changed it into what it currently is. Occasionalists believe that all events are caused directly by God. They argue that things that seem like efficient causes are really just results of a chain set in motion by God.
Interactionism is another philosophical theory that deals with the root causes of things. Those who adhere to this philosophy believe that a mental event can be the cause of a physical action and vice versa. For example, someone wants to kick a wall, so they do (mental to physical). Or, conversely, someone kicks a wall, so they feel pain (physical to mental). This theory is primarily focused on the way the body and mind interact with one another.
Parallelism is another philosophical theory of mind-body interaction. This one differs from interactionism in a key way. The parallelist believes that mental and physical events can run on a parallel course of existence, but that they do not interact in any way with each other. This theory relates more closely to occasionalism. Both theories refuse to tie causality to a verifiable mind-body interaction.