In a long time ago, there was a big area called the Polish-Lithuanian Commonwealth. This area had many different people living in it, and it was very important for all of them to be able to work together and agree on things.
One way they did this was by having something called "offices". This is like a special group of people who were put in charge of certain tasks. For example, there was an office in charge of making sure everyone was following the same laws, and another office in charge of helping people who were in trouble.
These offices were really important because they helped keep everyone in the Polish-Lithuanian Commonwealth safe, happy, and working together. They also made sure that everyone had a fair say in things, no matter what language they spoke, what religion they followed, or where they came from.
So, in summary, offices in the Polish-Lithuanian Commonwealth were groups of people who were in charge of different tasks and helped keep everyone working together and being fair to each other.