Plack is a kind of tool that helps people use different types of software languages (like Perl) to create websites that can be seen on the internet. It's like when you use blocks to create a tower: you need some help to make it stay together and not fall down. Plack helps the different parts of the website talk to each other so they can all work together and not fall apart.
Think of it like a playground where different kids can play together. Plack is like the teacher who helps the kids play nice and share the toys. It makes sure that everyone has a turn and no one is left out. In the same way, Plack makes sure that different parts of the website get to work together smoothly so that people can use the website without any problems.