Flu, short for influenza, is a contagious respiratory illness caused by influenza viruses. It can infect the nose, throat, and sometimes the lungs, leading to mild to severe illness. The flu is different from the common cold, and it usually comes on suddenly. It's most common in the fall and winter months, spreading through droplets when people cough, sneeze, or talk.

Common symptoms of the flu include a high fever, chills, muscle aches, tiredness, headaches, a sore throat, a runny or stuffy nose, and cough. Some people may also experience vomiting and diarrhea, though this is more common in children than adults. Symptoms can be intense and typically last about one to two weeks, though some people might feel tired for longer.

Treating the flu involves plenty of rest, staying hydrated by drinking lots of fluids, and taking over-the-counter medications to relieve symptoms like fever and aches. In some cases, doctors may prescribe antiviral medications that can make the illness milder and help you feel better faster. It's important to stay home to avoid spreading the virus to others, and always consult a healthcare provider if symptoms are severe or if you are at high risk for complications.