In the hallmark Wisconsin Central Ltd. v United States case, the Supreme Court of the US first mentioned about bitcoin in its judgment.
“Moreover, what we view as money has changed over time......our currency originally included gold coins and bullion, but, after 1934, gold could not be used as a medium of exchange; perhaps one day employees will be paid in Bitcoin or some other type of cryptocurrency. Nothing in the statute suggests the meaning of this provision should be trapped in a monetary time warp, forever limited to those forms of money commonly used in the 1930's.”
The case did not deal with bitcoin's legal meaning so it is not a binding definition of money in the US (In the language of common law lawyers it is an obiter dicta, the Latin term that means “things said by the way”).
Having said that, the obiter dicta of the US supreme court can be quoted in other common law jurisdictions. While it is not binding in other common law jurisdictions, judges in these jurisdictions may take into account of obiter dicta of other common law jurisdictions.
How many common law jurisdictions do we have in the world? There are many that are highlighted in pink below.
Source: Wikipedia