Zachary N. answered 03/20/22
SAT/ACT English Tutor w/ Political Science Background
A government shutdown means that as a direct result of Congress failing to fund the government bureaucracy on time, federal agencies that are considered "non-essential" are quite literally shut down. These non-essential employees, determined individually by their employers, are furloughed, meaning they do not report to work and do not get paid. On the other hand, essential employees are required to report to work but do not get paid (in 2019, Congress passed legislation that ensured the employees receive back pay for their work). This can result in many adverse affects on the country. Since the employees aren't getting paid, many choose not to show up to work, which can negatively affect various essential services, such as tax processing, airport security screening, food inspection, and welfare application processing.
The government mandates that certain services and programs that are deemed essential continue to receive funding regardless if Congress passed a spending bill on time. These services and programs include the military, welfare, airport security, border security, and law enforcement, to name a few. This is so the country isn't vulnerable internationally or suffers massive economic losses, but this isn't to say that there aren't serious effects stemming from a government shutdown.
For more information: https://www.crfb.org/papers/qa-everything-you-should-know-about-government-shutdowns#Whatservices