Cyril Northcote Parkinson first coined Parkinson's Law in The Economist in 1955. Later he put it in his book Parkinson's Law: The Pursuit of Progress. The Parkinson's law states that: Work expands so as to fill the time available for its completion.

Generalization
"Parkinson's Law" could be generalized further still as:
The demand upon a resource tends to expand to match the supply of the resource.

An extension is often added to this, stating that:
the reverse is not true.

This generalization has become very similar to the economic law of demand; that the lower the price of a service or commodity, the greater the quantity demanded.

Corollaries to Parkinson's Law
Data expands to fill the space available for storage.
Computer executable code fills CPU resource.
"Parkinson's second law": "Expenditures rise to meet income".
No amount of computer automation will reduce the size of a bureaucracy.
If you wait until the last minute, it only takes a minute to do - If a task can expand to fill the time allotted, then conversely, the effort given can be limited by limiting the allotted time.
You will fill up as much (storage) space that you have available to you" - you will acquire enough "stuff" to fill up the storage space that is available to you.
The amount of time in which one has to perform a task, is the amount of time it will take to complete that said task.

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