Electric current is the flow of electric charge in a conductor. It is the movement of electrons through a closed circuit. When a potential difference, also known as voltage, is applied across a conductor, it creates an electric field that pushes the free electrons in the conductor, causing them to move from the negative terminal to the positive terminal of the voltage source. The flow of electrons constitutes an electric current.

Explanation:
1. Electric current: Electric current is defined as the flow of electric charge per unit time. It is measured in amperes (A).
2. Flow of electrons: In a conductor, the flow of electric current is due to the movement of electrons. Electrons are negatively charged particles that are loosely bound to their atoms. When a potential difference is applied across a conductor, the negatively charged electrons are repelled by the negative terminal and attracted towards the positive terminal. This movement of electrons constitutes the flow of electric current.
3. Other particles: While protons and neutrons are also present in atoms, they do not flow as electric current. Protons are positively charged particles and are tightly bound to the nucleus of an atom. Neutrons are neutral particles and do not carry any charge. Only electrons, due to their mobility, can move freely in a conductor and contribute to the flow of electric current.
4. Direction of current: The direction of electric current is opposite to the direction of electron flow. Conventionally, the direction of current is considered from the positive terminal to the negative terminal of a voltage source. This convention was established before the discovery of electrons when it was believed that positive charges moved. However, it is now known that electrons are the mobile charge carriers.
5. Importance of electrons: Electrons play a crucial role in the functioning of electrical devices and circuits. The flow of electrons allows electric energy to be transferred from the source to the load, enabling the operation of devices such as light bulbs, motors, and electronic gadgets.
6. Conductors and insulators: The flow of electrons and the ability to conduct electric current varies in different materials. Conductors, such as metals, have a large number of free electrons that can easily move and carry electric charge. Insulators, on the other hand, have very few free electrons and do not allow the flow of electric current easily.

In conclusion, electric current is the flow of electrons through a conductor. Electrons, being negatively charged and mobile, are able to move in response to a potential difference, resulting in the flow of electric current. Protons and neutrons, on the other hand, do not contribute to the flow of electric current.