Failure to retrieve: this type of forgetting occurs when information that has been acquired at some point in the past is not accessible. The information that is unable to be retrieved is typically stored long-term memory.

 

Example: John met a girl 10 years ago that he dated. Her name was Jill. One day he tells his friend about the girl he dated but is unable to recall what her name was.

 

Resources:

http://www.simplypsychology.org/forgetting.html

http://psychology.about.com/od/cognitivepsychology/tp/explanations-for-forgetting.htm