In physics, a physical object (or body) is a collection of masses, which you look at as one object only. It applies to both living and non-living things.

A human's and animal's physical body is made up of organs and tissues. It is a part of a total living being, and might include its behaviour and way of thinking.

The point of the term is to include those systems which are separate in one sense. but connected in another sense. A galaxy has many different parts, but can be treated as a whole for some purposes. Likewise, a group of galaxies can be treated as one gravitationally. The Solar System is another example.

In general language it is usual for "object" to mean a physical boundary {border}, but a "system" to mean a group of connected objects.