Depending on context, the term may be used in several ways as follows.
Any User's Machine
A desktop PC can refer to any user's machine, whether Windows, Mac or Linux or style of case. However, the term "PC" by itself would be more common for this generic usage, and the terms "Windows desktop," "Mac desktop," etc. would be more specific. See
desktop computer.
Client vs. Server
The desktop PC is a client (the user's machine) in contrast to a network server. See
desktop computer,
client and
server.
Stationary vs. Portable
The desktop PC is a user's computer in a desktop or tower case in contrast to a portable computer. See
laptop and
tower case.
On the Desk vs. the Floor
A desktop PC may refer to a unit that is designed for the top of the desk, such as an all-in-one or a very small case, in contrast to a floor-standing tower. See
tower case and
all-in-one.