Okay, so imagine you have a toy box full of toys. You love playing with them and trying out new things, but one day you start feeling bored because you've tried everything and nothing seems new or interesting anymore.
Well, that's kind of what happened in Russia in the 1970s. They had a leader named Brezhnev who had been in charge for a long time, and things started feeling a bit stale and boring. People were still going to work and doing their jobs, but they weren't really excited about it.
The economy wasn't doing really well either. It's like if you had some money to spend on toys, but you kept buying the same ones over and over because there weren't any cool new ones coming out. So people didn't really have much to look forward to or get excited about.
This period of time where things felt kind of stuck and not really moving forward became known as the "Brezhnev Stagnation." It's kind of like if you were standing in one place for a really long time and not moving - it gets pretty boring after a while!