These are specific energies that an electron in an atom or other system can have. Like different grades in school - 9th, 10th, 11th and so on.
Population Distribution: This is the spread of people across various categories or groups. Like how students are spread across different grades in school.
Thermal Excitation: This is when particles gain energy and move to a higher energy state due to heat. It's like moving up a grade after passing your final exams!