The integers are discrete.
All finite sets are discrete.
I was part of discrete mathematics. Mathematics is crudely divided into discrete mathematics and continuous mathematics. Continuous mathematics is the part of mathematics based on the real number line, which is continuous. Algebra I and II, Precalculus, Calculus and Differential Equations are all courses in continuous mathematics. You've spent five or six years studying continuous mathematics, and now you're returning to pick up threads you left behind around grade 7.