Linear does not mean "graph is a line". It means "graph is a line through origin" (in the 2d case).
Somewhat counterintuitive, but that's how it's defined.
Somewhat counterintuitive, but that's how it's defined.
> In mathematics, the term linear function refers to two distinct but related notions (...) [proceeds to specify them using incomprehensible math words]
GNU Units documentation uses the second notion, common with linear algebra (and thus arguably more common in any computing) - the notion that calls y=ax a linear function, and y=ax+b an affine function.