A Baal Teshuva is a Jew who was not always religious but at some point in life changed and became a Torah Observant Jew. A FFB (Frum from Birth) is a Jew who was born into a religious family and has always lived a Torah life.
There are many differences between these two types of Jews. One of the most telling is whenever I ask a Baal Teshuva, "Are you behaving yourself?" he seems a little insulted that I should ask. He looks at me and answers, "Of course I am!" And whenever I ask a FFB the same question he always smiles, looks up a little and answers, "Oh, if only I could."