What does testing positive for HIV mean? What is meant by the window period? How does a false positive relate to it?

A window period is a recommended waiting period to receive an accurate HIV test result. Generally, it is a six-week to six-month period from the moment of your last unsafe sex encounter to the moment that you receive a HIV screening. This is the time your body uses to create antibodies in the blood stream, which signify exposure to HIV. This process is known as seroconversion.
It is important when receiving an HIV test to ask what kind of test is being used. Whenever someone is screened for HIV, two types of tests are used. They are, 1) a reactive test, and 2) a confirmatory test. A reactive HIV test indicates if HIV antibodies are in the blood (such as the Elisa Test). A reactive test may give a false positive reading to anyone with kidney or renal failure, to a woman that has had multiple pregnancies, anyone receiving the influenza vaccine, or to anyone that has received gamma globulin. When a reactive test has a negative result, that means no HIV antibodies were detected. But in order to receive an accurate reading, the CDC recommends you wait a specific window period: six weeks to six months and either abstain from all sexual activity, or practice safe sex in every sexual situation, and then get a confirmatory test, such as the Western Blot Test.
A confirmatory test (such as the Western Blot) provides the HIV status of a person. A positive test result on a confirmatory test means that the person has been infected with HIV, has HIV antibodies in his or her blood, and can infect others.