There have been three conflicts in the late 20th century and early 21st century called the Persian Gulf War; two are occasionally referred to as the Second Gulf War:

• Iran-Iraq War (1980-1988) (aka Persian Gulf War, First Gulf War). This was a war between Iraq and Iran following in the wake of the 1979 Revolution in Iran and triggered by Iraq's invasion of Iran.
• Persian Gulf War (1990-1991) (aka First Gulf War, Second Gulf War). This was a war between Iraq and a coalition of nations led by the United States in response to Iraq's invasion of Kuwait. The war was, in effect, sanctioned by the United Nations, and is technically a U.N.-led invasion of Iraq, rather than a U.S. one.
• the 2003 Iraq War (2003) (aka Second Persian Gulf War, Third Persian Gulf War). This was a war between Iraq and a coalition of nations led by the United States, which resulted in the removal from power of the government of Saddam Hussein.

The labelling of these wars as 'First', 'Second', etc. depends on the country and forces involved. For example Within the UK's Royal Fleet Auxiliary (RFA) the Iraq-Iran war is commonly referred to as the First Gulf War, whilst in the Royal Navy this term is more commonly used for the 1990-1991 war.