Synchronous data flow means things happen at the same time. Like when you play a game with your friend, you both take turns at the same time. You don't have to wait for your friend to take their turn before you take yours.
In computer technology, it means different parts of a program or system work at the same time. Each part does its job and then sends the information to the next part, like a relay race. This helps make the system work really fast and efficiently.
Think of it like a line of people passing buckets of water to put out a fire. Each person has their own job of passing the bucket to the next person. If someone is slow or misses a turn, the others will have to wait and the fire may get bigger. But if everyone passes the buckets at the same time, the fire can be put out faster. Just like how synchronous data flow in computers works to make things run smoothly and quickly.