Scalar: A quantity that has only one property: magnitude (or value). For example, the temperature only needs to be specified in terms of its value, such as 350 K or 25 ºC, etc.
Vector: A quantity that has two properties; magnitude and direction. For example, 30 km/h to the West is velocity, a vector quantity.
Watch the video below to learn more (credits-TED-Ed):
Actually, both scalars and vectors are special cases of a general class of quantities, known as tensors. More on tensors in a future post.