A few butterflies and many moth species spin a silk case or cocoon prior to pupating, while others do not, instead going underground. A butterfly pupa, called a chrysalis, has a hard skin, usually with no cocoon.
4. tension - (physics) a stress that produces an elongation of an elastic physical body; the direction of maximum tension moves asymptotically toward the direction of the shear. natural philosophy, physics-the science of matter and energy and their interactions; his favorite subject was physics.
Medical Definition of Tension. Tension: 1) The pressure within a vessel, such as blood pressure: the pressure within the blood vessels. For example, elevated blood pressure is referred to as hypertension. 2) Stress, especially stress that is translated into clenched scalp muscles and bottled-up emotions or anxiety.