Intermediate scrutiny, in U.S. constitutional law, is the second level of deciding issues using judicial review. The other levels are typically referred to as rational basis review (least rigorous) and strict scrutiny (most rigorous).
In order to overcome the intermediate scrutiny test, it must be shown that the law or policy being challenged furthers an important government interest by means that are substantially related to that interest. That should be contrasted with strict scrutiny, the higher standard of review that requires narrowly tailored and least restrictive means to further a compelling governmental interest.
Constitutional Equal Protection analysis applies not only to challenges against the federal government, but also to state and local governments. Although the Fourteenth Amendment's Equal Protection Clause applies only to state and local governments, the United States Supreme Court has implied an Equal Protection limitation on the federal government through a process known as "reverse incorporation." As the Fourteenth Amendment applies directly to the states, the incorporation process was unnecessary to hold this restriction against state and local governments. Equal Protection analysis also applies to both legislative and executive action regardless if the action is of a substantive or procedural nature. Judicially crafted (common law) rules are also valid only if they conform to the requirements of Equal Protection. See, e.g., Reed v. Campbell, 476 U.S. 852 (1986).
In the context of sex-based classifications, intermediate scrutiny applies to constitutional challenges of equal protection and discrimination.