true macro!

So what makes a macro lense a true macro?

I always presumed a prime lens with 1:1 magnification but there have been 1:2 macro lenses.

AFAIK anything up 1:2 is considered Macro; for example the legendary CZ Makro planar 100mm F2 ZK does 'only' 1:2

I've always understood that macro means that a subject (e.g. 1 cm fly) will be that same size (or bigger) on the sensor or film. So that would mean 1:1

I however have never seen an 'official' definition. One old book that I have states that one enters macro territory at 1:10; I would definitely not consider that real macro.

wikipedia states:
The other point is that true macro lenses are / can be optimized for performance at the highest magnification

again wikipedia:
But does it actually matter what the definition is or what real macro is? Check the specs of the lens and if the magnification (at short distance) is good enough for the intended use, it does not matter if it's called macro or not

Usually 1:1, but because a 1:4 Zoom lens can be printed easily
at 1:1 (4x enlargement) that can be called a macro as well

I thought it was as Sterretje says, same size image on the capture medium. I thought manufacturers altered that (unofficial but generally accepted) definiton so they could assign macro capabilities to compacts.

As somebody on the other forum often says: "printing 'macro' on a lens costs less ink than printing 'close-up'"