The discipline of engineering involves the application of math and scientific evidence to invent, design, maintain, and, in many cases, improve structures, machines, and systems. In other words, engineering applies knowledge in the sciences to create new things and improve old things.
Engineering is extremely broad, but it includes many different specialized kinds of engineering. These specialized disciplines include: chemical engineering, civil engineering, electrical engineeering, and mechanical engineering.
Each of the four main branches above has additional, more specific branches that one can get into. This includes biomolecular and materials engineering for the chemistry branch, structural and transport engineering for the civil branch, computer and optical engineering for the electrical branch, and acoustical and vehicle engineering for the mechanical branch. Additionally, there are various interdisciplinary branches one can delve into, including aerospace engineering, agricultural engineering, biomedical engineering, industrial engineering, nuclear engineering, and military engineering, among other branches.