Final answer:
The term for knowledge that you can't recall when it is needed is forgetting. It can happen due to various reasons such as encoding failure, absentmindedness, blocking, or amnesia.
Step-by-step explanation:
The term for knowledge that you can't recall when it is needed is forgetting. Forgetting refers to the loss of information from long-term memory. It can happen due to various reasons such as encoding failure, absentmindedness, blocking, or amnesia. Retrieval is the act of getting information out of memory storage and back into conscious awareness. These processes are essential for memory formation and recall.