Tegra is a family of systems-on-chip (SoC) for mobile devices, designed and sold to device manufacturers by NVIDIA, including one or more ARM CPU cores, a specially-designed NVIDIA GPU, among other components.
Tegra SoCs are usually found in mobile phones and tablets. See NVIDIA's Tegra site for specs, and some examples of products powered with Tegra processors. So far there have been three iterations of the Tegra family, named numerically.
This tag is very likely to be found in conjunction with arm, and sometimes 
android.
