A more thorough explanation:

The Espionage Act is a federal law that makes it illegal to engage in espionage, spying, or related activities. It includes two separate acts that were passed in 1917 and 1918.

The 1917 Espionage Act criminalizes false statements that are intended to interfere with the war effort, cause dissension in the armed forces, or obstruct national recruiting and enlistment activities. This act is still enforceable when the United States is at war.

The 1918 Espionage Act criminalizes speech that is intended to obstruct war-bond sales, generate scorn or contempt for democratic government, the flag, or the uniform of the Army or Navy, urge reduced production of war materials with the intent to hinder the war effort, or express support for a national enemy or opposition to the United States' cause.

For example, if someone were to publicly express support for a terrorist group that is an enemy of the United States, they could be prosecuted under the Espionage Act. Similarly, if someone were to spread false information about the military with the intent of causing dissent, they could also be charged under this law.

The Espionage Act is an important tool for the government to use in protecting national security, but it is also controversial because it can be used to limit free speech and punish dissent. The constitutionality of the act has been challenged in the past, but it has been upheld by the Supreme Court.