The answer to what does ttyl mean?, is that this initialism stands for 'Talk to you later'. It is used in chat between people to address that you'll be back in some time. Ttyl was popularized in the internet chat forums in the 1980s and 1990s. Even though these shortenings are often said to be the indicatives of the modern age, these types of short forms are getting used for a very long time. Some, such as OMG, date back to the 20s and RIP, being used for hundreds of years now.