What is meant by content source, crawler, indexer, query source and content type in SharePoint ?

i dont really know the answer i was sharePoint administrator but for 3 month only so as i remember the content source need crawlers and indexers to make the search more efficent , faster , and get spacific results

Crawler or Spider: This is a bot to collect documents on the Web.
Indexer: A software analyzes documents and generates searchable indexes for the documents.
Query Server: A system responses to user query and returns relevant documents.
http://ecommerce.insightin.com/search_engine_marketing/how_search_engines_work.html