Definitions of depth:

• noun:   degree of psychological or intellectual depth
• noun:   extent downward or backward or inward

  Example: "The depth of the water"

• noun:   (usually plural) the deepest and most remote part

  Example: "From the depths of darkest Africa"

• noun:   (usually plural) a low moral state

  Example: "He had sunk to the depths of addiction"

• noun:   the intellectual ability to penetrate deeply into ideas