Short answers, pulled from the story.
Memory is the faculty of the mind by which data or information is encoded, stored, and retrieved when needed. It is the retention of information over time for the purpose of influencing future action. Without it, language, relationships, and personal identity could not develop.
Memory is often understood as an information processing system made of a sensory processor, short-term or working memory, and long-term memory. Sensory memory holds information for less than one second, short-term memory allows recall for several seconds to a minute, and long-term memory can store far larger amounts for up to a lifetime.
Declarative or explicit memory requires conscious recall and includes semantic memory for facts and episodic memory for personal events. Procedural or implicit memory is not based on conscious recall but on implicit learning, such as remembering how to ride a bike or tie shoelaces, and it depends on the cerebellum and basal ganglia.
In 1956 George A. Miller, working at Bell Laboratories, put the capacity of short-term memory at seven plus or minus two items. Modern perspectives revise the figure down to roughly four or five items, or argue for a flexible limit based on information rather than items. Chunking can increase how much is held.
In a 1974 study by Elizabeth Loftus and John Palmer, people who were asked how fast cars were going when they smashed into each other gave higher speed estimates than those asked when the cars hit each other. A week later the smashed group was twice as likely to report seeing broken glass that was not in the film. The misinformation effect shows that misleading information can distort what people remember.
The Venus flytrap, native to the subtropical wetlands of the eastern United States, shows a rudimentary memory by closing only when two trigger hairs are stimulated within thirty seconds. This memory is not stored in a brain but in cytoplasmic calcium levels, where an initial subthreshold influx must be joined by a second influx to cross threshold and snap the trap shut.