Information Retrieval (IR) studies the discovery of information from unstructured knowledge sources such as text documents. This may be contrasted with retrieval from databases, where information is formally ordered. In other words, if your free text query can not find a relevant document in a collection you probably have a poor query. However, if your database query returns with nothing you know there was nothing there.
Web searching is part of IR, as is text classification, message routing, topic spotting etc.