Concept

A mental representation of a category of events consisting of the category's essential characteristics.

Sleep is a concept that some have considered to have at least the following characteristics:

• alternating stages of lighter and deeper sleep that cycle throughout the night and in which dreaming typically does not occur frequently;
• a stage of sleep in which the cerebral cortex is very active and dreaming occurs frequently.

Memory is a concept that some have considered to include at least the following characteristics:

• a short-term component that holds onto information for less than about 15 seconds (unless attention remains focused on it);
• a long-term component that holds onto information for minutes to years.