What is, "object of a preposition."
This site will help.
http://www.ucalgary.ca/UofC/eduweb/grammar/course/speech/1_5a.htm
Simply, the noun following a preposition is the object.
( the rabbit ran) over the HILL, under the LOG, and behind a ROCK.
Hill, log and rock are noun objects. The preposition shows the relationship between the verb and those noun objects.
Thank-you
Thank-you for answering one of my previous questions.
Thank-you GuruBlue