Linear vs non-linear is a confusing terminology. Linearity is a relationship. Anyway, usually it means values are encoded in the sRGB color space (with sRGB primaries) without applying any "gamma" curve (also bad term).
Like subb said, "sRGB Linear" means sRGB primaries without the sRGB EOTF (gamma curve) applied, which you could say is "raw linear" values, the most common way to input colors in 3d applications.