Adopt vs Undefined - What's the difference?

As a verb adopt

is (with relationship specified) to take by choice into relationship, child, heir, friend, citizen, etc.

lacking a definition or value.

(en verb)

(with relationship specified) To take by choice into relationship, child, heir, friend, citizen, etc.

(with relationship implied by context) To take voluntarily (a child of other parents) to be in the place of, or as, one's own child.

A friend of mine recently adopted a Chinese baby girl found on the streets of Beijing.

(with relationship implied by context) To obtain (a pet) from a shelter or the wild.

We're going to adopt a Dalmatian.

(with relationship implied by context) To take by choice into the scope of one's responsibility.

This supermarket chain adopts several families every Yuletide, providing them with money and groceries for the holidays.

To take or receive as one's own what is not so naturally.(rfex)

* '>citation

To select and take or approve.

to adopt the view or policy of another

These resolutions were adopted .

(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