9mm Largo is 9x23, but be careful not to confuse it with the 9x23 Winchester. They have the similar dimensions, but the 9mm Winchester cartridge is loaded to a higher pressure and is not safe to fire in a pistol designed for the 9mm Largo.
9x23
Assuming you mean 9mm, and not calibre, you have a number of options. There's the 9x19 Parabellum/Luger, the 9x17 (more commonly known as the .380 ACP in the US), the 9x18 Makarov, the 9x21, the 9x23 Steyr, 9x23 Winchester, 9x25 Mauser 'Export', 9x25 Dillon... quite a variety to choose from. Most likely, you'd be referring to a 9x19 firearm (also known as 9mm Luger or Parabellum).
The .380 ACP is 9x17, the 9mm Makarov is 9x18 (it should be noted the projectile for this round is actually 9.3 millimetres in diametre, as well), the 9mm Parabellum/Luger is 9x19. 9x21 is a commercial round intended for countries in which military calibres are prohibited for civilians to possess, and there are a few different 9x23 cartridges - 9x23 Winchester, which is fairly popular as an alternative to .38 Super for competitive shooting, 9x23 Steyr was a military cartridge which fell out of favour, and no current production firearms are manufactured for this cartridge. 9x25 Dillon is a 10mm casing necked down to a 9mm projectile, the 9x25 Mauser was a military cartridge which saw only limited service, and, like the 9x23 Steyr, no modern firearms are currently manufactured for this cartridge. Some also like to refer to the .357 Sig - which is a .40 S&W casing necked down to accept a 9mm projectile - as the 9x22, but this is in no way official, and it's typically referred to as .357 Sig, even in metric system countries. It should be noted that in the US, most of the time when someone refers to a 9mm, they're talking about the 9mm Luger (9x19mm Parabellum)
A bullet with a diameter of approximately 9mm. Not all 9mm projectiles are exactly 9mm in diameter - the 9x19 Parabellum/Luger has a diameter of 9mm, while the 9x18 Makarov has a diameter of 9.27mm, the 9x23 Steyr has a diameter of 9.03mm, etc.
No. Not all 9mm cartridges are the same. 9x19 (a.k.a., 9mm Luger, 9mm Parabellum), for example, is different, hence, not compatible with other 9mm cartridges, such as the 9x17 (a.k.a., .380 ACP), 9x18 Makarov, 9x21, 9x23 Mauser, etc.
The .380 ACP is a type of 9mm... 9x17, and is sometime referred to as the 9mm Short or 9mm Kurz. It is NOT the same as the 9mm Luger/Parabellum (9x19), and it is NOT compatible with any other type of 9mm cartridge (such as the 9x19 Luger/Parabellum, 9x18 Makarov, 9x21, 9x23, 9x25, etc.).
No. There are several different calibers that are called 9mm. These calibers are not interchangeable. A quick rundown of 9mm pistol cartridges: 9x17 also called 9mm Kurz, 9mm Short or .380 Auto 9x18 Makarov, also called 9mm Makarov 9x19 also called 9mm Luger, 9mm, 9mm Para, 9mm Parabellum 9x21 also called 9mm IMI 9x23 also called 9mm Long, 9mm Largo
There are several different types of 9mm cartridge. When Snoop Dogg or some other rapper talks about his "nine", they're referring to a weapon firing the 9x19 cartridge, also known as the 9mm Parabellum or 9mm Luger. Other 9mm cartridges in common use include the 9x17, which is also known as the .380 ACP, and the 9x17 Makarov cartridge, which is popular with military surplus collectors. There have been several other 9mm cartridges made, both past and present, to include the 9x23, 9x25, 9x39, etc.
The .380 ACP is a 9mm cartridge - 9x17mm. That is the ONLY cartridge which can be fired from a .380 pistol, and the 9x18mm Makarov, 9x19mm Parabellum/Luger, 9x21, 9x23, 9x25, etc. cartridges are NOT compatible. The Makarov cartridge actually uses a 9.3mm projectile, which is too large for the .380, and the 9x19 cartridge uses too long a case, meaning you won't get proper headspacing in the chamber, and it's designed for a locked breech pistol, generating too much pressure to be safely used in an unlocked breech pistol such as a .380. Do not attempt to use any ammunition other than what your firearm is intended to shoot.
There are several types of 9mm cartridges. .380 ACP is the commercial designation in English/Imperial system countries for the 9x17 cartridge (also known as the 9mm Short, and 9mm Kurz). This is the only cartridge which is to be fired from a weapon chambered for it, and other 9mm rounds are notinterchangeable. This includes the 9x18 Makarov, 9x19 Parabellum, 9x23 Largo, etc..380 pistols typically use an unlocked breech, which can be done given the generally low chamber pressure produced by the .380/9x17 cartridge. Now, a 9mm Parabellum cartridge would probably not even chamber in a .380, but, if it did and was fired, the considerably higher chamber pressure produced by that round could destroy the gun and cause serious injury to the operator.