1: The most common meaning of enlightenment is the historical period where people began to switch their beliefs from blind belief in religion to logic and common sense, or in other words: science. When Adorno and Horkheimer talk about enlightenment, the goal is seen to be more or less the same: to "liberate human from fear and install them as masters", where fear was being caused by myths, fantasy etc.. Here, enlightenment is referred to rather as a state of mind than as a historical period, a state where one strives for replacing beliefs with knowledge. But as man seeks to do this, the authors mean that he becomes a slave to his own quest of mastering nature, leading to a darker and more critical view on enlightenment.
2: Myths are explanations of the unknown without any logical foundation. For example, the melting of the arctic ice is explained by science as a result of rising temperatures, which in turn is a result of a chain of explanations etc.. A myth might state that the arctic is melting because the polar bears are hethens for worshiping a false god and are being punished by having their homes slowly destroyed. The goal of a myth is to eliminate fear by giving people something to believe in. The authors also mean that science is more or less modern myths, as it became worshiped by people who can't explain it's statements themselves.
3: The difference between "old" and "new" media is quality vs quantity and the nature of the interaction. "Back in the days", before media was delivered to a wide mass, it was primarily made to make people think. People read books, newspapers and looked at thought provoking art. New media is made for consumption, to fill an empty spot in ones mind and make money in the process. It has also made the communication one-way, making radio and television part of the new media. The latter notion is slowly fading away, as social media today has allowed consumers to make their voices heard. The consumption nature of media is definitely still true today though, almost 70 years after the books publication.
4: Just as the automobile industry makes automobiles for profit, the culture industry makes culture for profit. The focus in rather on the profit part rather than on culture. Producers of mass media make content for consumption of the wide mass, leaving little room for critical thinking or creativity. This is connected to the notion of the enlightenment, as the mass producers know how consumers work and what they want, they can produce content which more or less works as a bug light: attracting mindless victims killing of their time and ability to think.
5: Continuing on the previous question, mass deception is the notion of us being fooled to believe that we get what we want. Consumers are given an illusion of choice. An example from the modern time is the cinema-business. At any given time there are several movie productions consumers can choose to go to, but chances are high that they are all following the same formula with different variables put into them. This can be applied to many different medias today, and I guess this is what the authors were predicting in the book.
6: I found the notion of mass deception to be interesting, as I've been thinking about it before from different perspectives. I don't watch television for the same reason what makes mass deception to be what it is: everything follows the same formula. I'd be lying if I said I don't consume any media created for the wide mass at all, but I try to be more selective of my consumption than "what's on the tv schedule" or listen to what's on the radio. I've seen this notion developing in some areas of culture and reducing in others.
The reducing example: companies behind gaming platforms (Steam, Sony and Microsoft primarily) have been making it easier for independent producers of games to express themselves through productions (also called indie games) by making their mass-aimed platforms available for said production houses to distribute their games and hence making them able to contribute with (hopefully) new ideas and being able to make a living on it.
Increasing example: the latest years the EDM-scene (electronic dance music) has exploded, and the music which once was only played in underground clubs was suddenly being exposed everywhere from the radio to massive festivals around the globe. But this has turned the music from being a creative outlet for artists to a strive to create the most public-pleasing sound. Although it hasn't quite reached the same scale as other "older" mass-media, it's still heading down the same road.
I'll end this post with a concrete example of what I was trying to explain in the previous paragraph. Below is a mix of 16 "EDM festival anthems" with 4 seconds from each song, which aims to illustrate my point of everything sounding the same.