Liquid White and Liquid Clear are the names of two of the oil painting mediums created for painters following the Bob Ross Wet-on-Wet Technique®.
As the name suggests, liquid white is a fluid paint, with a consistency that's more like cream than the buttery paint you get from a tube. This means it's easy to apply and mix with other colors, both on and off the canvas. It is often used as the first layer in a painting, to create a surface for immediate wet-on-wet painting.