If you are not a U.S. citizen, you need to be "admissible" when entering the United States from abroad. (Permanent residents also don't need to worry about being admissible to the United States, most of the time.) I think admissibility is something that intuitively makes sense to most people. But not everyone thinks about it before planning a trip or immigrating to the U.S. Most of the emphasis is on...do I need a visa? And, how do I apply for a visa? The immigration process is long and expensive, and so is the process for some temporary United States visas (certain employment-based visas, for example). And so the importance of a traveler's admissibility becomes apparent. After all, wouldn't you want to know if you are going to have a problem getting a visa (or possibly being detained at a U.S. airport) before you spend thousands of dollars on a visa application or a green card?
I was excited to write my first article for the Worldwide Employee Relocation Council ("WERC") on the topic of admissibility--or rather, inadmissibility as U.S. immigration laws speak more directly about what makes you not admissible to the United States. You can find the article here: https://www.worldwideerc.org/news/public-policy/the-role-of-admissibility-in-us-immigration
Somewhat related, for a quick review of what U.S. Customs and Border Protection looks for when you go through immigration, see my YouTube I-Minute video: https://www.youtube.com/watch?v=QsvvYoF8nUU
