Queries can be navigational (the user has a single site in mind, the official homepage of a company/product), informational (searching for information), transactional (trying to obtain something: buy a product, download a video) or a combination of these categories. Depending on the query, search results can be: vital (for navigational queries with a dominant interpretation), useful (comprehensive, authoritative resources), relevant (pages that don't cover all the aspects of a query), not relevant (marginally related to the query) or off-topic.
Google thinks that there must be a connection between queries and search results in terms of generality: broad queries are best matched by broad pages, specific queries by specific pages. Search results must take into account the dominant interpretation of a query in a certain location and at a certain moment.
Spam is treated separately from search results evaluation. A web page may be spammy even if it's considered "vital" for some queries or it's very authoritative. "Webspam is the term for web pages that are designed by webmasters to trick search engine robots and direct traffic to their websites," explains Google. Web pages that include ads and scraped content from other sites, but don't bring any original information are considered spam. "When trying to decide if a page is Spam, it is helpful to ask yourself this question: If I remove the scraped (copied) content, the ads, and the links to other pages, is there anything of value left? If the answer is no, the page is probably Spam."
{ via Google Blogoscoped and SEO Book }
