The opposite of asynchronous. When clicking to load a regular webpage you then have to wait for the page to load before you can do anything else. This process is called synchronous as operations will only happen after the previous one is complete.
console.log('one'); countToAMillionAndSayYes(); console.log('two'); console.log('three'); // one // yes // two // three
In the above examples the console will log one after another and even though the 'countToAMillionAndSayYes' function will take a while, the last two consoles have to wait for it to finish before they can execute.