From the standpoint of Physics, it’s negative to positive. The particle responsible for electricity, the electron, has a negative charge. In, for example, a battery, the negative terminal has an excess of electrons and the positive terminal has a deficit. When the two terminals are connected, the electrons begin flowing from the negative to the positive (then back to the negative, internally in the battery).
From the standpoint of electronics, however, it doesn’t matter. You can imagine the electricity flowing from negative to positive or from positive to negative, and (in every case that matters to electrical engineers) you’ll get the same results every time. This is why some applications to electronics were discovered even before the charge of the electron was known, and why many electronics textbooks will talk about electricity flowing from positive to negative. Also, in electronics diagrams, things like diodes and transistors are drawn as though electricity flows from positive to negative.
When discussing positive to negative flow, electrical engineers will sometimes discuss positively charged particles flowing. In this case, they don’t mean protons or positrons: they’re talking about the flow of "space lacking electrons" or "electron holes" – gaps in space where there are no electrons even though there could be. These electron-hole "particles" are not actual particles; they’re simply a tool used to help imagine positive-to-negative flow.
As more of a physicist, I will discuss electrons, which flow from negative-to-positive and create a negative voltage when enough of them well up in one place, for the rest of this article. However, you can just as easily imagine everything in terms of electron-holes, which flow from positive-to-negative and cause a positive voltage, if that makes you more comfortable.
Additional Reading:
- How does jump starting a car work if current only flows when there’s a difference in voltage?
- How is it possible that there’s not a complete circuit to the power plant?
- (Un)Common Questions about Electricity
- Why can the resistor go at the beginning of the circuit OR at the end?
- How fast do electrons move in a circuit?
