Masquerade vs Undefined - What's the difference?

As a noun masquerade

is a party or assembly of people wearing masks, and amusing themselves with dancing, conversation, or other diversions.

is to assemble in masks; to take part in a masquerade.

lacking a definition or value.

(en noun)

A party or assembly of people wearing masks, and amusing themselves with dancing, conversation, or other diversions.

In courtly balls and midnight masquerades -

(obsolete) A dramatic performance by actors in masks; a mask. See “mask”

Acting or living under false pretenses; concealment of something by a false or unreal show; pretentious show; disguise.

I was invited to the masquerade at their home.

That masquerade of misrepresentation which invariably accompanied the political eloquence of Rome -

(archaic) A Spanish entertainment in which squadrons of horses charge at each other, the riders fighting with bucklers and canes.

To assemble in masks; to take part in a masquerade.

I'm going to masquerade as the wikipede. What are you going to dress up as?

To frolic or disport in disguise; to make a pretentious show of being what one is not.

He masqueraded as my friend until the truth finally came out.

A freak took an ass in the head, and he goes into the woods, masquerading up and down in a lion's skin -

To conceal with masks; to disguise.

To masquerade vice - Killingbeck

(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