Superposition
Many types of waves, including electromagnetic waves, have the property that they can traverse the same space independently of one another. If this were not the case, we would be unable to see anything. Imagine you are standing at one end of a room in an art museum, trying to view a painting on the far wall and this property did not apply. The light waves from all of the paintings on the side walls crossing back and forth would disrupt the light waves coming directly to you from the painting you were trying to view, and the world would be nothing but a blur. All these electromagnetic waves do, in fact, additively combine their electric fields at the point where they cross. Once they have crossed, each wave resumes in its original direction of propagation with its original wave form. This phenomenon is called the property of superposition.