Discrete mathematics is the study of mathematical relationships between distinct or individual parts. Its primary focus can be simplified as the realm of the integer. The concepts from discrete math are directly applicable to computing concepts. This has caused a rise in its popularity, especially as a required area of study for computer science and programming careers.
Computers are based in binary. Their mechanical function depends on two things; the electrical current is there or it is not. Therefore, everything a computer can do, from turning on through complex calculations, stems from those electrical inputs. As that simple input is combined with others to form more complex pieces it still relies upon base two for its computations. Since it cannot have a fractional input of there or not, it is ideal for discrete mathematical concepts.
There are many integer based mathematical concepts that can be considered part of discrete mathematics. The following list are some of those, specifically as they apply to computing.
Rosen, K.H.(1999). Discrete Mathematics and its Applications. McGraw Hill.