A matriel that resists the flow of electrons is called what?

Such a material possesses property referred to as electrical resistance. Resistance is measured in Ohms. Elements developed with the purpose of causing a specific resistance in electrical circuits are called resistors.

The answer to your question could be "a resistor" but it could also be "an insulator" if they are asking about materials with a complete absence of conductivity (or, infinite resistance). Vaguely worded question.