The phrase "to melt the butter" means to soften or liquefy butter by heating it. This can be done in a variety of ways, such as placing the butter in a saucepan and heating it over low heat until it becomes liquid, or using a microwave oven to heat it for a short period of time. Once melted, butter can be used in various recipes or cooking methods, such as pouring it onto popcorn while making movie theater-style popcorn, or incorporating it into baking recipes.