Since the accepted answer here is incorrect, and daniel svenson's answer is mostly correct but lacking explanation, I will try to answer the question completely for future readers.
Since Mac OS 10.2 through at least 10.11, printing is handled by the CUPS system and this answer is the same. While drivers are typically found in
/Library/Printers, the folder can contain support files and many other things which are not themselves print drivers, and in the real world there is no canonical location within the folder where the actual driver files are stored.
The only authoritative list of available print drivers on OS X is that returned by
lpinfo -m (specifying the host is not necessary for the local machine). CUPS specifies that drivers can consist of an arbitrary number of files, but they must all be declared in a central PPD file.
lpinfo -m will parse any valid PPDs found; if it doesn't have a PPD that CUPS can parse, then it isn't a valid print driver. A sample of the output:
MacBook-Pro:~ user$ lpinfo -m
Library/Printers/PPDs/Contents/Resources/CNPZUD450ZU.ppd.gz Canon D400-450
Library/Printers/PPDs/Contents/Resources/CNPZUD490ZU.ppd.gz Canon D460-490
Library/Printers/PPDs/Contents/Resources/CN6300.ppd.gz Canon iPF6300(CUPS)
Library/Printers/PPDs/Contents/Resources/CN6300S.ppd.gz Canon iPF6300S(CUPS)
Library/Printers/PPDs/Contents/Resources/CN6350.ppd.gz Canon iPF6350(CUPS)
Library/Printers/PPDs/Contents/Resources/CN8300.ppd.gz Canon iPF8300(CUPS)
Library/Printers/PPDs/Contents/Resources/CN8300S.ppd.gz Canon iPF8300S(CUPS)
drv:///sample.drv/okidata9.ppd Oki 9-Pin Series
drv:///sample.drv/okidat24.ppd Oki 24-Pin Series
raw Raw Queue
Each line specifies the path to that driver's PPD file, followed by the display name of the printer as declared in the PPD. As you can see, some drivers are internal to CUPS and do not even have a PPD file in
lpinfo -m is the only way to be certain of everything available to the printing system.
Deleting a printer using the 'minus' button in System Preferences does not delete/uninstall the driver. It just deletes the queue that has been created for the printer in question. The 'Reset printing system...' option will also not remove any drivers; it just deletes all print queues and resets some CUPs configuration options to defaults.
Deleting one of the PPD files listed by this command will effectively delete the driver, as it will no longer be loaded/accessible by the CUPS system, though as explained above there may be additional support files left behind. There is no standard way to remove these because each driver can include support files in different places, but there is no cause to delete them unless you are intending to reinstall the driver. In that case, the original installer package from the manufacturer should handle re-installation of all relevant files.
I have sometimes seen people manually copying PPD files as a means of installing printers; there is no guarantee this will work! Some drivers require only a PPD but some may need support files as well. The only way to be sure all necessary files are installed is to use the original installer package.