While there are many kinds of searches, most are concerned with either a novelty search or right to market search.
The novelty search looks for earlier published documents (prior art) that may anticipate and invention defined by the claims, or sometimes described in the specification, of a patent document. This type of searches typically undertaken when assessing registrability or validity or of a patent claim.
A right-to-market search looks for granted patents having claims that may prohibit exploitation (manufacture, export, import, sale or use) of a product or method in a jurisdiction. This is a specific search that must be conducted in relation to each jurisdiction where a product or method may be exploited.