The correct answer is option 'C' - Active window.

Explanation:
An active window refers to the object that is currently being used or displayed on the desktop. It is the window that is currently in focus and receiving input from the user. The active window is typically highlighted or has a different appearance compared to other windows on the desktop.

Here is a detailed explanation of each option:

a) Working window: This term is not commonly used in reference to windows on a desktop. It may refer to a window that is currently being used for work or a specific task, but it does not specifically indicate the window that is currently active.

b) Current window: This term could be interpreted as the window that is currently being displayed on the desktop. However, it does not necessarily imply that the window is actively being used or receiving input from the user.

c) Active window: This is the correct option. The active window is the one that is currently in focus and receiving input from the user. It is the window that the user is currently interacting with.

d) Processing window: This term does not specifically refer to the window that is being used or displayed on the desktop. It may imply a window that is currently undergoing some form of processing or operation, but it does not indicate that it is the active window.

e) None of these: This option implies that none of the given options accurately describe the object that is currently being used or displayed on the desktop. However, in this case, option 'C' - Active window is indeed the correct answer.

In summary, the active window refers to the object that is currently being used or displayed on the desktop. It is the window that is in focus and receiving input from the user.