The Rectangle SOP creates a 4-sided polygon. It is a planar surface.
/orient - Picks the major plane the rectangle's y-axis orients itself with. Set it to camera if it is to point towards a camera.
/camera - Specifies which camera to use if Orientation is set to camera.
/sizex /sizey - Adjusts the size of the rectangle in X and Y. sizex = 1 and sizey = 1 is scaled to fit the whole camera view if Orientation is set to camera.
/tx /ty /tz - These X, Y, and Z Values determine where the center of the Rectangle is located. Center is applied after the rectangle is properly oriented and is with respect to the camera view so X is always left/right, and Y is always up/down.
/camz - Camera Z is an arbitrary distance you specify from the camera. It will move the rectangle so it is this many units away from the camera, then scale the rectangle so it fills the viewer.
/texture - Texture addes (0,1) coordinates to the vertices when set to Face. Creates a rectangle without uv attributes when set to Off.
Inputs / Geometry Types
Bounding Source - If an input is used, a bounding box of its geometry is made, and the options Center and Size are disabled.