When we talk about the flow of charge in a closed circuit, we usually refer to the flow of electrons. Electrons are negatively charged particles, and they move from the negative terminal of a voltage source (like a battery) to the positive terminal. This movement of electrons constitutes an electric current.
The convention of current flow is established based on historical interpretations. In reality, electrons carry the negative charge and move from the negative to the positive terminal. However, when the concept of electric current was first introduced, the prevailing assumption was that positive charges (which are actually found in protons) were the carriers of current. This was known as conventional current flow.
So, even though electrons are the ones physically moving through the circuit, the direction of current flow is considered opposite, from positive to negative. This convention was established before the discovery of the electron, and it’s maintained for consistency and convenience in electrical engineering and circuit analysis. It’s important to keep in mind this convention when working with circuit diagrams and analyzing electrical circuits.