The highland charge was a way that Scottish soldiers attacked their enemies in battle a long time ago. Picture this - you're playing a game of tag with your friends, and you want to tag them really really badly. You don't just walk up to them and touch them, that's too easy. Instead, you run really really fast towards them, with your arms outstretched, hoping to tackle them and make them "it".
Well, that's kind of what Scottish soldiers did in battle. They would hold their weapons (usually swords or spears) in front of them, and run really really fast towards their enemies, with their arms outstretched. This way, when they got close enough, they could poke or slice their enemy with their weapon, and hopefully hurt them really badly.
This move was called the highland charge because it was frequently used by Scottish soldiers from the Highland region of Scotland. They were known for being really fierce in battle, and the highland charge was one of the ways they proved it.