The document discusses key concepts related to the unit circle and circular functions including: 1) the standard position of an angle places the initial side on the x-axis with the terminal side extending in the clockwise direction from the initial side, 2) reference angles which are the acute angles formed between the terminal side and the nearest x-axis, and 3) coterminal angles which are angles that share the same terminal side but can differ by full rotations of 360 degrees.