Basically when looking for an SSD, you use the specific model of MacBook Pro as the identifier.
For instance: SSD for late 2013 MacBook Pro. This is generally the Blade Type PCI-e SSD as seen in the links above.
For older MacBook Pros it may be a Sata 2.5" SSD,
For the newest MBPs its simply soldered to the motherboard so no type.
Unlike RAM, it does not get more specific, as for those any blade-type PCI-e SSD will generally fit.