Meaning:
Depending on who you ask, you’ll actually find an array of definitions for this odd idiom. Here are some of the most commonly used definitions:
1. There is evidence to back up a previously made claim, specifically evidence intrinsic to the object in question. (Example: Of course this project will be successful, the proof is in the pudding.)
2. The process of achieving something isn’t important as long as the end product is good. (Example: I may have had to walk 1,000 miles to find this treasure, but the proof is in the pudding.)
3. The success of something can only be measured by putting it to its intended use. (Example: You’ll have to try it out before you buy it, since the proof is in the pudding.)
Origin:
The reason for the plethora of definitions is most likely the Americanization of the old British idiom, which reads “the proof of the pudding is in the eating.” Whereas the British version makes at least some sense, the shortened American version is nonsensical. This led to the varied use of the idiom in a multitude of situations, with varying understandings of the definition. The British version, however, is closest in definition to the third listed above. The word
proof
was synonymous to
test
in the 16th century, which is when this idiom is thought to have surfaced. Pudding was also far different from today. It was most likely a minced-meat dish. Therefore, the true test of the success of a pudding dish is in how it tastes, not any ornamentation or appearance. More generally, the success of something can be measured only by putting it to its intended purpose. It is unknown where the more American definitions came from, though they are used very commonly.