Iron rice bowl is a term used in China to describe a job that provides its employees with very secure and stable employment. The term "iron rice bowl" refers to the fact that people with such a job will always have enough to eat, just as if they had an "iron rice bowl" that could not be broken.
Let's say that you have a bowl that is really strong and won't break no matter what you do to it. You can fill it up with rice and trust that it will always stay full. In the same way, people who have an iron rice bowl job can trust that their jobs will always be there and they will always have enough money to take care of themselves and their families.
The concept of an iron rice bowl job comes from a time when people relied on the government or large state-run companies for their employment. These jobs were incredibly secure because they were guaranteed by the government, and often offered things like pensions and other benefits. Even if someone was not very good at their job, they could still expect to keep it for a long time because of the job security that came with their iron rice bowl.
Nowadays, the term iron rice bowl is less common as China's economy has changed over the years, and traditional state-run companies have given way to private enterprise. But the idea of having a secure job that allows you to take care of yourself and your family is still important to many people, whether their job comes with a literal iron rice bowl or not.