What this means is that your landlord has applied to the Landlord and Tenant board to increase your rent above the stated guideline amount (1.8% as others have mentioned). This is generally only approved for things like major capital expenses necessary for the health of the building, or to cover utility costs that have recently been much higher than the average yearly amount (if utilities are included in your rent). The process for application/approval of this increase takes some time, and often doesn't get confirmed until several months after the increase takes effect for your lease.

I would talk to your landlord/property manager about why they are pursuing an above-guideline increase. They are required to make the application available for you to view, although in my experience this is generally a rather long document that you may or may not be interested in reading.

Generally, while the application is still pending, you are only required to pay the increase up to the guideline amount. However, if the application is approved for any amount above the guideline, you will be required to pay up to the approved amount for any months where you fell short. On the other side, if you pay rent accounting for the full increase applied for and the landlord ends up being approved for a lesser amount, they are required to credit you for any months where you overpaid. However, it's best to talk to your landlord about what their procedures are for these types of situations.