The null
The plain benchmark a strategy has to beat before anyone can say it works.
Every result needs something to be compared against. The null is that something: what you would have got without the idea. The obvious null, doing nothing, is too easy. Buying US stocks between 2009 and 2026 made money without any idea at all, so a strategy that made money in those years has not shown anything yet.
The right null keeps everything the idea did not contribute: the market drift, the calendar, the universe, the costs, and removes only the selection. Shuffling the signals builds that null. A long-short portfolio builds a similar one by cancelling the market between two baskets. When a logbook entry says "the null matters more than the result", it means that the same numbers can be a discovery or nothing at all, depending on what they are measured against.
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Where this word comes up
First needed in the log entry H-044 · Short-term momentum in large caps: no robust edge in our test.
From the same entry: Betting against losers, High turnover, Liquid names, Momentum, Multiple testing, Relative strength ranking, Shuffle test.