O
object
  (1) A computer representation of something that a user can work with to perform a task. An object can appear as text or an icon. (2) A collection of data and member functions that operate on that data, which together represent a logical entity in the system. In object-oriented programming, objects are grouped into classes that share common data definitions and member functions. Each object in the class is said to be an instance of the class.
object code
  Machine-executable instructions, usually generated by a compiler from source code written in a higher-level language (such as the C++ language). For programs that must be linked, object code consists of relocatable machine code.
object file
  (1) A file that contains compiled code. (2) A member file in an object library. IBM. Object files end with the file extension .obj (OS/2, Windows) or .o (AIX). Contrast with source file.
object library
  A file used to store object modules.
object module
  (1) All or part of an object program sufficiently complete for linking. Assemblers and compilers usually produce object modules. T. (2) A set of instructions in machine language produced by a compiler from a source program. IBM.
object-oriented programming
  A programming approach based on the concepts of data abstraction and inheritance. Unlike procedural programming techniques, object-oriented programming concentrates on what data objects comprise the problem and how they are manipulated, not on how something is accomplished.
octal
  A numbering system that uses eight digits, 0 through 7. It is used as a shorthand system for representing binary characters that use six bits.
open file
  A file that is currently associated with a file descriptor. X/Open, I.
operand
  An entity on which an operation is performed. I, A.
operation class
  A class that defines all elements and key operations required by a specific collection implementation.
operator
  A symbol (such as +, -, *) that represents an operation (in this case, addition, subtraction, multiplication).
operator function
  An overloaded operator that is either a member of a class or that takes at least one argument that is a class type or a reference to a class type. See overloading.
operator precedence
  In programming languages, an order relation defining the sequence of the application of operators within an expression. I.
optical reflective disc
  An optical videodisc that is read by means of the reflection of a laser beam from the shiny surface on the disc.
ordered collection
  (1) An abstract class that has the property of ordered elements. (2) In general, any collection that has its elements arranged so that there is always a first element, last element, next element, and previous element. Contrast with unordered collection.
ordering relation
  A property that determines how the elements are sorted. Ascending order is an example of an ordering relation.
overflow
  A condition that occurs when a portion of the result of an operation exceeds the capacity of the intended unit of storage.
overflow condition
  A condition that occurs when a portion of the result of an operation exceeds the capacity of the intended unit of storage.
overloading
  An object-oriented programming technique where one or more function declarations are specified for a single name in the same scope.
owner window
  A window similar to a parent window, but it does not affect the behavior or appearance of the window. The owner coordinates the activity of a window. See parent window.