Speculation can mean a great many things. However, it is generally used to refer to a statement or theory that may or may not be based entirely on fact(s) or evidence. Therefore, it can not be classified as canon or as an officially accepted truth until recognized by the subject's creator as "genuine."
Though the word may be thrown around a lot here, almost all known information regarding Death Note can be found in How to Read 13 and verified.
The word, as defined by dictionary.com:
spec-u-la-tion, noun, means:
- The contemplation or consideration of some subject: (i.e. To engage in speculation on humanity's ultimate destiny.).
- A single instance or process of consideration.
- A conclusion or opinion reached by such contemplation.
- Conjectural consideration of a matter; conjecture or surmise: (i.e. A report based on speculation rather than facts.).
- Engagement in business transactions involving considerable risk but offering the chance of large gains, esp. trading in commodities, stocks, etc., in the hope of profit from changes in the market price.
- A speculative commercial venture or undertaking.
-Mogturmen 22:57, 22 September 2008 (UTC)