In a criminal trial, a defendant is any person accused (charged) of commiting an offence (a crime), an act defined as punishable under criminal law. The other party to a criminal trial is usually a public prosecutor.
In a lawsuit, a defendant (or a respondent) is also the accused party, although not of an offence, but of a civil wrong (a tort or a breach of contract, for instance). The person who started the civil action through filing a complaint is referred to as the plaintiff.
(Terminology varies from one jurisdiction to another. The convention in Scotland does not recognise the use of the term "defendant" in criminal proceedings; the terms "accused" or "panel" are used instead.)
Defendants in civil actions usually make their first court appearance voluntarily in response to a summons. But criminal defendants are often taken into custody by police and brought before a court under an arrest warrant. Historically, civil defendants could be taken into custody under a writ of capias ad respondendum and be forced to post bail before being released. But modern-day civil defendants are usually able to avoid most (if not all) court appearances if represented by a lawyer. Criminal defendants are usually obliged to post bail before being released from custody and must be present at every stage of the proceedings against them. (There is an exception for very minor cases such as traffic offenses in jurisdictions which treat them as crimes.)
Most often and familiarly, defendants are persons: either natural persons (actual human beings) or legal persons (persona ficta) under the legal fiction of treating organizations as persons. But a defendant may be an object, in which case the object itself is the direct subject of the action. When a court has jurisdiction over an object, it is said to have jurisdiction in rem. An example of an in rem case is United States v. Forty Barrels and Twenty Kegs of Coca-Cola (1916), where the defendant was not The Coca Cola Company itself, but rather "Forty Barrels and Twenty Kegs of Coca-Cola". In current US legal practice, in rem suits are primarily asset forfeiture cases, based on drug laws, as in USA v. $124,700 (2006).
Defendants can set up an account to pay for litigation costs and legal expenses. These legal defense funds can have large membership counts where members contribute to the fund. The fund can be public or private and is set up for individuals, organizations, or for a particular purpose. These funds are often used by public officials, civil-rights organizations, and public-interest organizations.
England and Wales 
See also 
|Look up defendant in Wiktionary, the free dictionary.|
|Look up plaintiff, petitioner, claimant, or complainant in Wiktionary, the free dictionary.|
- O. Hood Phillips. A First Book of English Law. Sweet and Maxwell. Fourth Edition. 1960. Page 151.