Pinellas County is a county located in the state of Florida. As of the 2010 census, the population was 916,542. Its county seat is Clearwater, and its largest city is St. Petersburg. Pinellas County is included in the TampaâSt. PetersburgâClearwater, Florida Metropolitan Statistical Area.
Nowadays, we can say in plain English: A set is a well defined collection of objects. The elements or members of a set can be anything: numbers, characters, words, names, letters of the alphabet, even other sets, and so on.
Then our sets included integers. The universal set for that is all the integers. In fact, when doing Number Theory, this is almost always what the universal set is, as Number Theory is simply the study of integers. But in Calculus (also known as real analysis), the universal set is almost always the real numbers. And in complex analysis, you guessed it, the universal set is the complex numbers.