'Belt and Braces' is a Britishism.
In the USA, braces hold your teeth in place as you grow up, and suspenders hold up your pants.
In the UK, braces hold your trousers up - just like your belt does. (Pants are under your trousers, suspenders hold up ladies stockings, and buck teeth are considered sexy. :-)
So 'belt and braces' is a British term for conservative planning. It describes a design or plan that has several ready-made alternate parts and if any one of them works then the whole thing works.
Compare with Gerry Wienberg's Plait? Principle, FailSafe, FallBack?, WhatIsPlanB.
-- DickBotting
Of course, the US version of the phrase is BeltAndSuspenders, which, I assume, would be as amusing (or confusing) to a Brit as BeltAndBraces was to me.
In fact, this term has a particular meaning to me when I am coding. Sometimes, I have code which cleans out a temp table. The same code runs when the user of the temp table starts (usually with no effect, but "just to be safe") and when it ends (to minimize the "junk" lying around out there). Of course, one could (theoretically) eliminate one cleanup or the other but it actually seems more elegant and robust to me the way it is. Even better, I suppose, one could use a real database (with *real* temp tables) and never have this problem at all. In any case, I usually comment one end of the operation "belt" and the other end "suspenders", just to indicate that I know the two are redundant but that I did it on purpose.
-- JeffShelby
ExtremeProgrammingChallengeNineteen uses "BeltAndBraces" to mean "doubling-up on the test coverage to deal with pernickety driver situations".