# What is `Undefined`

?¶

In the last section we looked up the documention for `Undefined`

. What exactly is it?

To find it in the WMA docs we add the name after `https://reference.wolfram.com/language/ref/`

which gives https://reference.wolfram.com/language/ref/Undefined
It is listed as a “Built-in Symbol”. In contrast to the other examples and indeed most of the kinds of things you are likely to add, this one is not a function, but a “symbol”. The description for this is “a symbol that represents a quantity with no defined value”.

Asking in the Q/A section of mathics-core we learn that
`Attributes[Undefined]={Protected}`

.

Another place where you may be able to get information about Mathematica is StackExchange Mathematica and Wolfram Language

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