An electron is a tiny particle inside an atom which orbits the nucleus. Electrons have a negative charge, unlike protons, which have a positive charge. When the number of electrons in an atom equals the number of protons in an atom, the atom is neutral. Whereas protons and neutrons are held tightly inside the atom, electrons can move from one atom to another quite freely. Therefore, electrons, because they have the ability to move from one atom to another through touching, determine the charge of an atom and have the ability to change the charge of any atom.
Is it a fundamental particle?
Our first definition of a fundamental particle was a particle that could not be broken down any further. Protons, neutrons and electrons were put under this category. Now we know that all three of these particles can be split even further. Despite this, we still refer to protons, neutrons and electrons as the fundamental particles. These three particles combine to make up the atom.