A non-linear RGB colorspace, which approximates a gamma of 2.2. The vast majority of image editing programs and operating systems work in the sRGB colorspace by default. Therefore, most images you will encounter will be in the sRGB colorspace.
OpenGL has the ability to work with sRGB textures and screen images directly. Accesses to sRGB textures will return lRGB values, and writes to sRGB screen images can be converted from linear to sRGB values, so long as a proper enable is used.
The process of ensuring that all textures, images, and other sources and destinations of colors (such as vertex attributes) are either already in lRGB or are converted to/from the linear colorspace as needed. Textures in the sRGB format are part of that, but so is rendering to an sRGB screen image (or manually doing gamma correction). These provide automatic correction. Manual correction may need to be applied to vertex color attributes, and for proper interpolation, this correction needs to be applied before interpolation.