Before, when science wasn't as advanced, scientists believed that an electric current flowed from the positive end to the negative end of a circuit. However, more advanced technology has allowed scientists to investigate this more thoroughly, and results state that electric current flows from the negative terminal to the positive terminal, thus called the electron flow. For reasons unknown, scientists have maintained the original idea of the current running from the positive terminal to the negative one, and have named it conventional flow.
Before the structure of the atom was understood, scientists such as Benjamin Franklin believed that an electric current was a flow of some sort of mysterious 'fluid' that moved from an area of high pressure to an area of low pressure. The high pressure was considered to be 'positive' pressure and the low pressure was considered to be 'negative pressure'.
Even though we now know that (in metallic conductors, anyway) that current is a flow of free electrons from negative to positive, for some weird reason many textbooks still show current as flowing from positive to negative! To differentiate between the two current directions, we use the terms 'electron flow', and 'conventional (or 'Franklinian') flow'.