A more thorough explanation:

Intermediate scrutiny is a legal test used by courts to determine if a law is constitutional. It is used when a law negatively affects certain protected classes, such as gender or illegitimacy. To pass intermediate scrutiny, the law must further an important government interest and must do so by means that are substantially related to that interest. This test is less rigorous than strict scrutiny but more rigorous than the rational basis test.

• Gender Discrimination: In Craig v. Boren, the Supreme Court applied intermediate scrutiny to a statute that discriminated on the basis of gender. Since then, any law that discriminates based on gender must undergo the intermediate scrutiny test.
• Illegitimacy: According to Matthews v. Lucas and Trimble v. Gordon, laws that discriminate based on illegitimacy are also subject to intermediate scrutiny.
• First Amendment: Intermediate scrutiny is also used for certain First Amendment issues, such as regulating mass media, adult entertainment, and highway signs. For example, in US West, Inc. v. United States, the Ninth Circuit Court of Appeals used intermediate scrutiny for a federal statute that prohibited telephone companies from providing video programming to subscribers.

These examples illustrate how intermediate scrutiny is used to determine if a law is constitutional when it negatively affects certain protected classes or infringes on First Amendment rights. The law must further an important government interest and must do so by means that are substantially related to that interest. This ensures that laws are not discriminatory or overly restrictive of individual rights.