A type of memory containing information that is stored for periods ranging from about 30 seconds to many decades, often differentiated into episodic memory for events and experiences and semantic memory for information about the world, although perceptual memory may not fall into either category. Also called secondary memory. See also ACT*, declarative memory, episodic memory, levels of processing, procedural memory, semantic memory, working memory. Compare sensory memory, short-term memory. LTM abbrev.