A combination of substances that can be separated by physical means is called a heterogeneous mixture. Think of how oil and water can be easily separated from each other by physically pouring off the oil or how the sand and water of mud can be separated by physically drying it out. You will find a lot of heterogeneous mixtures in daily life. Even things like a salad where all of the ingredients are mixed but can be separated physically can be considered a heterogeneous mixture.
