The concept of a function of one or many variables (up to 4 independent variables , three for the spatial coordinates x,y,z (or ρ,θ,φ in spherical coordinates) and one for the time coordinate),
The concept of derivative of the function (partial derivatives in the case the function has many variables or simple derivative in the case our function has only one independent variable)
The concept of integral of a function (integral over a line or a curve, over a surface, or over a volume)
Almost all physical laws come in the form of differential equations (equations that contain functions and partial or simple derivatives of functions) or integral equations (equations that contain functions and integrals of the functions). The most typical example are Maxwell's Equations in classical electromagnetism which can be expressed both as partial differential equations and as integral equations.