APA Dictionary of Psychology

a process in which attention is diverted away from a target task, goal, stimulus, or internal state due to competing thoughts or mental activity; it can occur unintentionally (e.g., intrusive thoughts or worries) or be used intentionally as a strategy to manage negative emotions (e.g., anxiety), pain, or stress. Its effectiveness depends on personality, context, and the particular stressor. See also attentional focus.