I would be inclined to define mathematics as the study of "relationships" rather than "patterns" but they are obviously closely related(!). There is a field of mathematics called "category theory" that is just about as abstract as you can get (the textbook, in the preface, said category theory is often called "abstract nonsense" with no sense of that being derogatory at all). A category has "objects" and "relations". The collection of all sets is a category with sets as objects and functions between them as "relations". The collection of topological spaces is a category with the topological spaces being the objects and continuous functions from one topological space to another being the relations.
One basic theorem of category theory is that a category is completely defined by its relations- you don't have to mention the objects at all!
In fact "relationism" is a recognized philosophy of mathematics- it is a subset of the "Platonist" philosophy.
Here's another point, related(!) to that: Mathematical "structures", consist of: axioms, definitions, undefined terms, theorems etc. Back when I was in high school geometry, they explained the "undefined terms" by saying that a "definition" is an explanation in words- of course, you need to know the definitions of the words in that definition in order for it to make sense. Hopefully the words in a definition are simpler and more basic that then word they define. Eventually, you get back to the simplest possible concepts which cannot be "defined" because there are no simpler words.
That's perfectly good but it is only recently that I realized how very fundamental to mathematics "undefined terms" are. Mathematical structures are "templates" and the undefined words are the "blanks" that have to be filled to apply the template to a specific purpose.
Why is it that Calculus, originally developed to solve problems in physics (specifically the orbits of planets) can be used so effectively for problems in economics, biology, etc.?
All of calculus, like any mathematics, is based on theorems proved from axioms and definitions, both of those containing undefined terms. To apply it to any field, you give meaning to those "undefined terms" using terms of your application. If, then, you can show that the axioms are "true" in terms of your application, then you know that all theorems, and all methods of solving problems based on those theorems, still work!