Traffic refers to vehicles moving along roads and streets. When you hear about heavy traffic on the highway, it means many cars, trucks, and buses are all trying to use the same road at once, often moving slowly or stopping frequently. During rush hour, when people travel to and from work, traffic typically gets much heavier than it is in the middle of the day.

The word can describe the flow itself: “Traffic was light this morning” means few vehicles were on the road. It can also describe congestion: being stuck in traffic means you're barely moving because too many vehicles are crowded together. Cities work hard to manage traffic using signals, signs, and timing to keep vehicles moving smoothly.

Traffic also appears in other contexts. Air traffic controllers manage planes taking off and landing at airports. Internet traffic refers to data moving through computer networks. When a website gets lots of traffic, many people are visiting it. You might even hear about foot traffic in a store, meaning the number of customers walking through.