Okay, so sometimes people write important papers and books, but they don't make them available for everyone to read. This can make it hard for people who want to learn from those papers or use that information to make new discoveries.
Guerilla open access is when people try to make those papers and books available to everyone, even if the people who wrote them don't want that to happen. It's like sneaking into a movie theatre without paying so that you can watch the movie for free (though, we don't support doing that, just to be clear).
People who practice guerilla open access might do things like look for ways to get around paywalls or share copies of articles with others who can't afford to access them. They might use computer programs to find and download articles that are locked up behind expensive subscriptions. They might even create their own websites or databases where they can share these resources with others who might not have access to them.
Some people think that guerilla open access is really important because it helps to level the playing field and give more people access to knowledge that could really help them. Others think that it's not fair or legal to take someone else's work without their permission, even if it's for a good cause.
So, just like everything else, there are different sides to the guerilla open access debate. But it's definitely something to think about when we talk about who gets to learn and discover, and who gets left behind because they can't afford to pay for access to information.