Subliminal advertising is when advertisers try to control your brain without you even knowing it. They do this by sending messages to your brain that you can't consciously see or hear.
It's a bit like trying to trick your brain into doing something without you noticing. Sometimes they use images or words that flash really quickly on a screen, or they might put hidden messages in a song.
The idea is that if they can get into your brain without you realizing it, then they can make you want to buy their product without you even knowing why.
But don't worry too much, because subliminal advertising isn't very effective and it's actually pretty hard to do it properly. Most of the time, advertisers write messages in big bold letters or use catchy jingles to get your attention, so you can just enjoy your TV show or music without worrying about subliminal messages.