Electron cloud distribution
The electron cloud distribution describes the probability of finding an electron in some region of space around the nucleus at some instant of time.

Imagine you have a camera that can take close-up shots of a hydrogen atom showing the electron at an instant in time. Also suppose that camera can keep snapping pictures, say, a thousand times a second, each time on the same image so that you get a multiple exposure. As the camera runs, the multiple images of the electron will begin to form a cloud-like picture which is dense in some places and thin in others. For the single electron of hydrogen, the densest part of this cloud will form a sphere with the nucleus at the center. As you travel inward toward the nucleus, or outward away from the nucleus, the cloud will get progressively thinner.

The thickest regions of this cloud are thick because the electron was found there more often than in the thin regions. So, if we were to take just one snapshot, this is where the electron would be most likely be found. That is, the probability of finding the electron at a given time is greatest where the cloud is densest.

Other elecrton clouds in other element's atoms have different shapes. Do understand that this is a model that explains some chemical behavior but it is not the current "final" model of how electrons behave in atoms.