HARP stands for Home Affordable Refinancing Program. It's an Obama's program helping home owners with properties under water starting March 2009.

About The Home Affordable Refinance Program (HARP 2.0):
In October 2011, the Federal Housing Finance Agency (FHFA), Fannie Mae and Freddie Mac announced enhancements to the Home Affordable Refinance Program that make it easier for lenders to refinance HARP-eligible mortgages.

HARP program may help you refinance your investment properties too if the following conditions met:

1) You didn't miss mortgage payments.
2) You bought the investment property prior to 2009
3) The mortgage for this property have bought by Fannie Mae or Freddie Mac.

Check with your lender to see if your investment property is eligibile for HARP program and take this advantage with lower interest rate.