In an object-oriented programming language, what does an object represent?

Okay -

I like to think of an object as a concentrated data ball. An object is simply a representative embodied form of something, which has state and behaviour.

Behaviour is the actions it takes, and state is the properties it holds.

This can be explained with an example -

The car object has behaviour and state. One of the behaviours of the car object is its Acceleration() method. One of the states of the object is the Weight() property.

The Acceleration() method is an action, that being the action of acceleration. 

The Weight() property is the state, which is the weight of the car.

The weight is simply just something that the object knows about itself. It knows its weight. 

The acceleration is simply just something that the object does. It does accelerate. 

So all of these factors tie into an object. All of the behaviours and state are all stuffed in this little-concentrated data ball, which knows and does. =)