So imagine you're playing with blocks with your friend. You both have red, blue, and yellow blocks. But your friend has more blue blocks than you do, and you have more red blocks than your friend. This means you have a "minority" of red blocks compared to your friend's blue blocks.
Now, imagine if the blocks were people instead! In Lithuania, there are people who are Polish, but they are not the majority. They have a "minority" status because there are more Lithuanians than Polish people living there.
This can sometimes make things tricky, because the Polish people might feel like their language and culture isn't given as much attention as the Lithuanian language and culture. But both groups of people are important and deserving of respect!