Question

Jordan is frightened by the sound of a train whistle. the sound is a(n):

Answer 1

Jordan is frightened by the sound of a train whistle. the sound is a "Stimulus".

A stimulus is an effect from outside which affects an action or an activity, sometimes triggering some psychological response. For example in the given example the sound of the train is an external effect (Stimulus) which triggers the feeling of fright in Jordan.