Gun pills: why is it called a .38 Special?

Why the .38 Special is defined as "Special", and is  a .38, even if it shoots a .357 caliber bullet?

38 Super: The Semi-Auto .38 That's Slipping Into Obscurity

Colt, Page 2

Culture

38 Special Ballistics - Velocity, Energy & Bullet Drop

Is the Revolver Dead? - SkyAboveUs

Colt Detective Special - Internet Movie Firearms Database - Guns

Optics, Page 8

Hornady's new bullets and ammunition loads for 2016

Taurus 856 .38 Special Revolver Review - Guns and Ammo

A History of the Iconic .38 Special - The Shooter's Log

Is a .38 special revolver a dangerous or safe carry gun? - Quora

38 S&W Variants and History - Shooting Times