Fleece vs Undefined - What's the difference?

As a noun fleece

is (uncountable) hair or wool of a sheep or similar animal.

is to con or trick someone out of money.

lacking a definition or value.

(wikipedia fleece)

(uncountable) Hair or wool of a sheep or similar animal

(uncountable) Insulating skin with the wool attached

(countable) A textile similar to velvet, but with a longer pile that gives it a softness and a higher sheen.

(countable) An insulating wooly jacket

(roofing) Mat or felts composed of fibers, sometimes used as a membrane backer.

Any soft woolly covering resembling a fleece.

The fine web of cotton or wool removed by the doffing knife from the cylinder of a carding machine.

(fleec)

to con or trick someone out of money

to shear the fleece from an animal (such as a sheep)

(wikipedia undefined) (-)

Lacking a definition or value.

(mathematics, computing) That does not have a meaning and is thus not assigned an interpretation.

The result of division by zero is undefined .

* defined