png to mac conversion might in broad sense represent opening or working with PNG graphics on Mac computers and you have plenty of graphics editors available on Mac for that. Or it can be searched by users looking for a way how to convert png on mac, which is also doable, for example with the default Preview app.
In very specific sense, png to mac conversion is used for export of PNG graphics to MacPaint raster format (.mac), which was the graphic app on the original Macintosh computers. Some graphics tools still support these .mac files, but overall the support is limited at best.
