Scientific Realism is a way of looking at the world that explores whether science can tell us the truth about the way the world is. To put it simply, it's a way of thinking about science that says that science gives us an accurate view of reality. For example, if scientists study something in the natural world and figure out what it is made up of and how it works, then that is true about reality and it is something that we can trust.
Musgrave's scientific realism says that science is our best way of understanding the world, and that we can trust what science tells us. In other words, scientific knowledge is trustworthy, and it is the best way of understanding and learning about the world around us. Musgrave's scientific realism also encourages people to use their scientific knowledge to improve the world.