Lucene is a mechanism which does full text searching on a set of data. I don't know Lucene in detail, but most of these things basically make a big 'index' of the contents of documents, databases, other files, all kinds of stuff, and then let you do 'clever' searching on them, like finding records where two different terms are found close together. They generally also let you do 'facetted' searches, which are the kinds of things you get when you search Amazon or eBay - so after you search for 'trainers' you get choices which let you narrow it down to a colour or price range or other 'facets' that their pieces of information might have.
Hello - thanks for your reply. You have explained it very well. I wondered if you could tell me what some other types of search are, and the differences between them? Eg, I know that a Boolean search uses the connectors and/or/not.