keywords missing from Wikipedia

It looks like Wikipedia could be greatly strengthened by the simply device of adding a section of keywords to every article. Just because an article is replete with an entity doesn’t mean a search for that entity will include that article. A good example is the article on Euler’s four-square identity, which is replete with sums of squares, but does not contain the phrase ‘sum of squares’, and so a search for ‘sum of squares’ would not include the article on Euler’s four-square identity.
[wanted documentation feature]
[wanted documentation enhancement]
[missing feature]
[search criteria]