What is defined as improper entry by an alien under U.S. law?

Improper entry by an alien under U.S. law primarily involves scenarios where an individual who is not authorized to be in the U.S. attempts to enter or re-enter the country unlawfully. The correct answer highlights a specific aspect of this definition related to individuals who have been removed or deported from the U.S. and then attempt to return without proper permission.

When an alien who has previously been removed makes an attempt to re-enter the country, this action is explicitly defined as improper entry. It represents a violation of immigration laws because the individual has already gone through a legal process that prohibits their return for a certain period or until they obtain the necessary permissions.

In contrast, other options address different aspects of immigration violations. Assisting aliens in entering the U.S. may involve actions that are illegal, but they don't necessarily pertain directly to the definition of improper entry. Similarly, marriage fraud and the importation of aliens for immoral purposes involve different crimes related to immigration but do not fit within the specific category of improper entry as defined by U.S. law. Each of these actions addresses various legal issues, yet they do not encapsulate the core focus of reentry after removal.