How do you define a facet in Drupal? (As in faceted search)

There's two kinds of searches in Drupal.

The first is a keyword search, it's what you're used to with say, Google. Type a word or phrase and you see results that are related to that phrase.

The other search is called faceted search, which is what you might see if using the Best Buy website. You may select attributes about the thing you are searching for to refine your result set. For example, to say I'm looking for: an computer manufactured by Apple, with a screen size of 15", priced less than $3000, which is on sale--here your are doing a faceted search.

The facets in this case are: manufacturer, screen size, price, and sale-status

You can combine these searches to use keyword, and then further refine by facets.

Each facet has items, take the manufacturer for example, it's items are:

apple
dell
compaq
...

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