Armstrongism is a kind of religious belief that started with a person named Herbert W. Armstrong. Some people who follow Armstrongism believe that they are part of a special group chosen by God to learn the truth about things. They follow a lot of rules and try to live their lives the way they think God wants them to.
One big thing that Armstrongism teaches is that God has a plan for everything and that the end of the world is coming soon. They believe that the Bible has secrets that only they can understand, and they use these secrets to try to predict when the end of the world will happen.
Armstrongists also believe that they should avoid some things that other people enjoy, like eating certain foods, celebrating some holidays, and even going to certain kinds of doctors. They think that these things are not good for them and will make it harder for them to be close to God.
Overall, Armstrongism is a religious belief that some people follow to try to get closer to God and prepare for the end of the world.