In physics, there are two kind of quantities that have a vital roles in order to explain the phenomena encounter in the real world.
The two quantities are: scalar and vector.
definition:
A scalar is a quantity that has a magnitude only. example of scalar are: pressures, length, mass, intensity, energy, electric potential, and so on.
A vector is a quantity that has both a magnitude and a direction. example of vector are: force, displacement, velocity, acceleration, linear momentum, electric field, magnetic field, and so on.
sometimes, in the books, the temperature is classified as a scalar quantity but it is not as simple as that.
What is a symbol for a scalar and a vector?
A symbol for scalar usually is a letter without any changes or stand alone. For example: a body has a mass m, electric potential is V, energy is E, and so on. while for a vector the symbol should be a bold letter both a small or a capital letter. For example: a force usually given the symbol F or F with an arrow exactly above of that letter. (see the figure.)


Note: in this time and to the future we use both the former or the later one interchange.