Tuberculosis (TB) is an infectious disease caused by the mycobacterium tuberculosis bacteria. It is spread through droplets from coughs or sneezes of someone who has an active infection. TB most commonly affects the lungs but can also affect other parts of the body.
Not everyone who gets infected with TB gets sick. You can be infected with TB but have no symptoms; this is called Latent TB.  If you have Latent TB and develop TB symptoms, then it is considered to be Active TB. Active TB can be fatal if not treated with the proper antibiotics.