A differential form is an expression involving differentials that can be used to approximate changes in a function. It allows for the linear approximation of how functions change with respect to their variables.
Derivative: A measure of how a function changes as its input changes, represented as $f'(x)$ for single-variable functions.
Linear Approximation: An estimation of the value of a function near a given point using its tangent line.
$dx$: A notation representing an infinitesimally small change in the variable $x$.