We can call the light streak that appears on the paper in the experiment as a light beam. However, we should note that the light beam is purely invented by physicists - they do not exist in nature.
Why did we invent them?
Rays of light show the direction in which the light travels. Since we also see and know that light travels in a straight line, we also understand where the light came from.
Applying this knowledge in this experiment, we get an image that describes the light from a point light source.
We can ask, how many rays are reflected from one point light source? We picked three and drew them. If we had placed the slit system a little differently, we would have obtained an image with slightly shifted rays. If we were to draw the rays from all the possible locations of the slits in the house, we would end up with one area densely packed with rays, which is the same spot of light we started the exercise with.