When grown-ups talk about the 1973-75 recession, they're referring to a time when lots of people were having a really hard time finding jobs and making ends meet. It happened because there was a big problem with how much money factories and businesses were making. During that time, things like fuel and supplies that factories used to make products cost a lot more money than usual.
People also started buying fewer things because they didn't have as much money, which made factories and businesses make even less money. That meant that some of them had to close down or lay off workers, which made things even harder for everyone.
It was like if you had a lemonade stand, but suddenly the lemons and sugar you needed cost a lot more money than usual, and nobody was buying your lemonade anymore. You might not be able to afford to keep making lemonade, and you might have to close your stand or let your helpers go.
Thankfully, things eventually got better as people started buying more things and businesses started making more money again. But it was a tough time for a lot of people.