Magnum or Sig.
A 357 magnum is a very long cased 9mm bullet with a magnum load behind it. Very powerful, very effective. Most commonly found in revolvers. I only know of one Semi-Automatic that fires .357 mag and that's the Desert Eagle.
The other is a Sig. designed by Sig Sauer. The 357 Sig. is basically a .40 caliber casing necked down to a 9mm. This is to produce space where the "magnum load" can be stored in a semi-automatic pistol. Giving both the quality of a 357 magnum and the quantity of a .40 caliber pistol. I believe this is the new standard issue weapon for D.P.S. Officers.