GNU Linear Programming Kit, or GLPK for short, is a computer program that helps solve problems where you want to use math to find the best solution to a problem. Let's imagine you want to bake some cookies, but you only have a limited amount of ingredients. You could use GLPK to help you figure out exactly how much of each ingredient you need to use to make the most cookies possible.
Now, GLPK works by taking all the information you give it - like the amounts of flour, sugar, and butter you have - and using a special type of math called linear programming to figure out the best solution. Linear programming is like a really fancy way of drawing lines that can help you find the best answer to a problem.
The great thing about GLPK is that it's totally free, so anyone can use it to solve problems or make decisions. And even though it uses complicated math, you don't need to be a math genius to use it - all you need to do is tell it what you want to figure out and give it the right information.