Structuralism in the philosophy of mathematics is the view that mathematics is primarily concerned not with the intrinsic nature of individual mathematical objects, but with the relations and patterns that hold between them. On this view, what matters in mathematics is the structure: the network of roles objects play within a system. For instance, the number 2 does not have some metaphysically unique essence; it is simply the element that comes after 1 and before 3 in the natural number structure. If another system has elements that play the same roles (such as two strokes, or two apples), that system instantiates the same structure. Thus, mathematical truth is understood as truth about these abstract structures rather than about standalone objects.
Structuralism contrasts with views that treat mathematical objects as independent entities (like Platonism) or as mere linguistic or mental constructions (like formalism or intuitionism). Structuralists argue that what makes mathematics objective and widely applicable is that the same structure can be realised in many different domains. The real focus of mathematics, therefore, is the invariance of relationships under change of the underlying objects. This perspective helps explain why mathematics is so general and transferable: it studies forms of organization rather than the particular things being organized.
Sources
https://plato.stanford.edu/entries/structuralism-mathematics/