What does one month "OP" mean

It means it's a one month rental fee that the "Owner Pays". Traditionally, the renter pays the brokerage fee of 15% of the annual rent.

Traditionally, yes, the renter pays 15%, but even in a good market it was easy for any renter not using his own broker (so the broker is just on the owner's side) to negotiate one month, not 15%. One month is ~8%, so it works out better for the owner's broker than to split 15%.

In any case, anyone renting these days should be pushing HARD for the owner to pay the fee and should even try to negotiate other concessions like termination rights, first partial month free to handle moving logistics, etc. There is NO good reason in a market like today for a renter to pay a broker fee.

There is no fee since I went straight to the building rental office. I guess the OP was put up there for brokers use - not renters use. Bummer - was hoping to get a free month

Here is the example
http://www.streeteasy.com/nyc/rental/433700-rental-401-east-34th-street-midtown-east-new-york

It's an incentive offered by buildings. OP does indeed mean "owner pays" -- so one month "OP" is usually either one month to the broker or 13 months for the price of 12. I think what your building did to you was to use the "OP" budget to lower your monthly rent over the course of 12 months, isn't that about the deal they gave you?

ali r.
{downtown broker}

No. The rent was not prorated. I called cantor and they said it's only meant for brokers oh well I tried. I really want that free month. The apt I showed above is the same as mine but on the 30th fl. Mine is on 5 and. 200 cheaper for now