What is the meaning of the term "search" in the context of the Fourth Amendment?

The Fourth Amendment forbids an unreasonable search by the government. A search has been authoritatively defined as occurring " `when an expectation of privacy that society is prepared to consider reasonable is infringed.' " United States v. Karo, 468 U.S. 705, 712 (1984) (quoting United States v. Jacobsen, 466 U.S. 109, 113 (1984)). The term "search" is thus not itself a helpful term on which to focus. A court's attention is directed to the "expectation of privacy" and society's view of the reasonableness of the expectation.