Anisotropic filtering (AF)
Anisotropic Filtering is a type of texture filtering which increases the visual quality of textures at steep angles to the camera, such as those that recede into the distance.
The option to enable Anisotropic Filtering is present is almost every PC game on the market today. Usually you will be able to select texture sample rates of 2x, 4x, 8x, or 16x. The texture sample rate is the number of passes the Anisotropic Filtering algorithm makes on the current textures in the frame. Most newer GPUs can render settings of 8x or 16x AF without a noticeable loss of performance, but if you are experiencing low FPS, lowering the sample rate or disabling the Anisotropic Filtering setting may increase performance.