Nowadays most free-text searching is based on Lucene-like approaches, where the search text is parsed into its various components. For every keyword a lookup is done to see where it occurs. When looking for a couple of keywords this approach is great. But what about it if you are not looking for just a couple of keywords, but a 100,000 of them? Like, for example, checking against a dictionary?
This is where the Aho-Corasick algorithm shines.