Episodic memory is the form of long-term memory that consists of your memories of your life. Psychologists
distinguish it from semantic memory, which consists of your general
world knowledge. As the term implies, episodic memories are memories for
specific episodes--specific events in your life. Thus, your
memory of your last birthday party, your last argument with your parents,
or your last biology lecture are all episodic memories. Your
knowledge of language and arithmetic are all semantic memories.
Endel Tulving, the psychologist who first came up with the term, says
that an episodic memory involves "being conscious of a prior conscious
experience." In other words, if you can remember the original experience
happening to you, it's an episodic memory. If you can't, then it's a
semantic memory.
Why is this distinction important? Well, some research showed that
amnesic patients lost episodic memories but did not lose semantic memories. Patients with Alzheimer's disease, for example, lose the ability to store and retrieve episodic memories. Some recent research suggests that semantic memory is impaired too, but the issue isn't settled yet.
On a neurobiological level, episodic memory seems to depend on the medial temporal lobes, especially the hippocampus, as well as the frontal lobes. | 
