p

padding: Some padding bytes are inserted in the data stream to maintain alignment of the protocol requests on natural boundaries. This increases ease of portability to some machine architectures.
parent window: If C is a child of P, then P is the parent of C.
passive grab: Grabbing a key or button is a passive grab. The grab activates when the key or button is actually pressed.
pixel value: An n-bit value, where n is the number of bit planes used in (that is, the depth of) a particular window or pixmap. For a window, a pixel value indexes a colormap to derive an actual color to be displayed.
pixmap: A three dimensional array of bits. A pixmap is normally thought of as a two dimensional array of pixels, where each pixel can be a value from 0 to (2ⁿ)-1, where n is the depth (z axis) of the pixmap. A pixmap can also be thought of as a stack of n bitmaps.
plane: When a pixmap or window is thought of as a stack of bitmaps, each bitmap is called a plane or bit plane.
plane mask: Graphics operations can be restricted to only affect a subset of bit planes of a destination. A plane mask is a bit mask describing which planes are to be modified, and it is stored in a graphics context.
pointer: The pointing device attached to the cursor and tracked on the screens.
pointer grabbing: A client can actively grab control of the pointer, and button and motion events will be sent to that client rather than the client to which the events would normally have been sent.
pointing device: Typically a mouse or tablet, or some other device with effective dimensional motion. There is only one visible cursor defined by the core protocol, and it tracks whatever pointing device is attached as the pointer.
pop-up: One of the uses of a top-level shell (for example, a menu that pops up when a command button contact is activated). Setting the state of a shell to :mapped is sometimes referred to as mapping or popping up the shell. Setting the state of a shell to :withdrawn or :iconic is sometimes referred to as unmapping or popping down the shell.
property: Windows can have associated properties, consisting of a name, a type, a data format, and some data. The protocol places no interpretation on properties; they are intended as a general-purpose naming mechanism for clients. For example, clients might share information such as resize hints, program names, and icon formats with a window manager via properties.
property list: The list of properties that have been defined for a window.
pseudo color: A class of colormap in which a pixel value indexes the colormap to produce independent red, green, and blue values. That is, the colormap is viewed as an array of triples (RGB values). The RGB values can be changed dynamically.