Object
Also called Object model
In AP Physics an object is a physical thing whose internal structure and properties are ignored. Calling something an object is a modeling decision: it says the thing has mass and position but no size, no shape and no moving parts.
College Board defines the term in its appendix, Vocabulary and Definitions of Important Ideas in AP Physics, as a physical thing where the internal structure and properties of the thing are ignored. AP Physics 1 EK 1.2.A.1 says the same thing in course language: when using the object model, the size, shape and internal configuration are ignored, and the object may be treated as a single point with extensive properties such as mass and charge.
The appendix's example is a truck. A driver does not think about the engine, the doors, the wheels, the frame or the suspension. The truck is one thing. Model it as an object and it looks the same from the top, the bottom or the side, and there is no difference between pushing its top and pushing its bottom, because the location where a force is applied is not part of the model.
Which is exactly when the model breaks. Load the truck with unsecured bricks and the bricks' motion starts to matter. Put a wheel on an axle and ask about its rotation, and the object model cannot tell you that a point near the rim moves faster than a point near the hub. At that stage the CED switches to a rigid system.
One nuance looks like a counterexample. Friction depends on the surfaces of two things in contact, so it seems to need internal structure. The appendix answers that two blocks may still be modeled as objects, because the friction force between them does not depend on their size or shape.
A system of several objects can itself be treated as a single object when the parts' behavior does not affect the analysis, which is EK 2.1.A.2.