Hi Tim! "Rent" is the money one pays to the landlord. It is not usually used with "a". Example: "I have to pay the rent tomorrow." "Did you pay the rent?" Because the speaker is talking about his/her specific rent payment, "the" is used with the noun. "Renting" is the progressive form of the verb "to rent". This word isn't used as a noun in American English, so it won't need "a". Example: "I am renting an apartment in the city. "A rental" is a noun for any house, apartment, trailer, car, boat, bike, etc. that is available for rent. A person may pay rent to use it for a specific length of time. Example: "That house is a rental." "My car is a rental." I hope this helps!