It seems like every function/process can be "linear" given the right basis. e.g. the function x**2 is linear in the state space which includes polynomials of degree 1 to n. Similarly, a process like exponential growth appears non-linear in the sense that if I plot Y = a* exp(r * x), the line is curvy; however, the same plot looks "linear" if I plot it on a log axis.
A lot of people talk about something being linear or non-linear, and I'm not sure what this really means.
On a terminology note, is there such a difference between a linear/nonlinear "process" and a linear/nonlinear "function", or can function/process be used interchangeably in this context?