What are inquiries and how do they affect my FICO score?

 Credit inquiries are requests by a "legitimate business" to check your credit.

As far as your FICO score is concerned, credit inquiries are classified as either 

"hard inquiries" or "soft inquiries"

Only hard inquiries have an effect on your FICO score.

Soft inquiries are all credit inquiries where your credit is not being

reviewed by a prospective lender. These include inquiries where

you're checking your own credit (such as checking your score in my FICO).

Credit checks made by businesses to offer you goods or services (such

as promotional offers by credit card companies), or inquiries made by

businesses with whom you already have a credit account.

Hard Inquiries are inquiries where a potential lender is reviewing your credit

because you've applied for credit with them. These include credit

checks when you've applied for an auto loan, mortgage or credit

card. Each of these types of credit checks count as a single

inquiry. One exception occurs when you are "rate shopping". That's

a smart thing to do, and your FICO score considers  all inquiries within a

45 day period for a mortgage, an auto loan or a student loan as a

single inquiry.

This same guideline also applies to a search for a rental property such as an

apartment. These inquiries are usually recorded by the credit bureau as a type

of real estate-related inquiry, so the FICO Score will treat them the

same way. You can avoid lowering your FICO Score by doing your

apartment hunting within a short period.