It refers to the region or space in which there is a high probability of finding an electron in atom.*NucleusElectron cloudEnergy sub-levelAtomic orbital

The term that refers to the region or space in which there is a high probability of finding an electron in an atom is the "Atomic orbital".

Here's a step-by-step explanation:

1. Nucleus: This is the center of the atom, which contains protons and neutrons. Electrons are not found in the nucleus, they orbit around it.

2. Electron cloud: This is a term used to describe where electrons are when they go around the nucleus of an atom. But it doesn't specify the high probability region.

3. Energy sub-level: This refers to the energy levels found within an electron shell. These are labeled s, p, d, and f. While these do describe where an electron could be, they are not the most specific term for the high probability region.

4. Atomic orbital: This is a term used to describe the space where an electron can be found 90% of the time. Each orbital can hold a certain number of electrons and the shape of the orbital can tell us about the electron's behavior. Therefore, this is the term that best fits the description.