Strep is short for streptococcus, a type of bacteria that causes several common infections. The most familiar is strep throat, which makes your throat extremely sore, often with white patches on your tonsils and a fever. Unlike the scratchy throat you get from a common cold, strep throat hurts intensely when you swallow and usually requires antibiotics prescribed by a doctor.

Strep bacteria are surprisingly powerful for something microscopic. They spread through coughs, sneezes, and shared drinks. When a doctor suspects strep, they'll swab your throat and test it, because strep throat needs different treatment than viral infections. Left untreated, strep can occasionally cause more serious problems, which is why doctors take it seriously.

You might hear someone say they “tested positive for strep” or that “strep is going around school.” While strep throat is miserable, antibiotics usually start to help within a day or two, and many people feel noticeably better soon after beginning treatment.