Heterogeneous mixtures that never settle are called colloids. Colloidal dispersions, as they are known in chemistry, remain evenly distributed without settling out. Examples include butter, milk, smoke, fog, ink and paint.
Colloids are not the only type of heterogeneous mixture. The other type, characterized by particles that eventually settle, are known as suspensions. A common example of a suspension is a puddle of muddy water. Left undisturbed, the dirt eventually settles to the bottom.
Homogeneous mixtures where one component dissolves entirely into the other, such as sugar in a glass of water, are known as solutions. These, like colloids, never settle. The difference between colloids and solutions (and between heterogeneous and homogeneous mixtures in general) is that the particles in solutions are very small, often less than a nanometer in diameter. In colloids, the particles are substantially larger.