1. A set is a well-defined collection of objects called elements or members that are represented using curly brackets.
2. There are different types of sets including the empty set which has no elements, the singleton set which has a single element, finite sets which have a finite number of elements, and infinite sets which have an infinite number of elements.
3. Other key concepts discussed include equal sets which have the same elements, subsets which have elements that are contained within another set, the power set which is the set of all subsets, and the universal set which contains all elements of other sets discussed.