elisp: Autoload Type
2.3.17 Autoload Type
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An “autoload object” is a list whose first element is the symbol
‘autoload’. It is stored as the function definition of a symbol, where
it serves as a placeholder for the real definition. The autoload object
says that the real definition is found in a file of Lisp code that
should be loaded when necessary. It contains the name of the file, plus
some other information about the real definition.
After the file has been loaded, the symbol should have a new function
definition that is not an autoload object. The new definition is then
called as if it had been there to begin with. From the user’s point of
view, the function call works as expected, using the function definition
in the loaded file.
An autoload object is usually created with the function ‘autoload’,
which stores the object in the function cell of a symbol. 
Autoload, for more details.
Info Catalog
elisp: Byte-Code Type
elisp: Programming Types
elisp: Finalizer Type