Scalar quantities are defined by their magnitude alone, such as temperature or mass, while vector quantities include both magnitude and direction, like velocity or force. The discussion highlights confusion around the use of positive and negative signs in scalar quantities, emphasizing that these signs indicate value relative to a reference point rather than direction. For example, a temperature of +10°C and -10°C represents values on a scale without implying directional movement. Understanding these distinctions is crucial for correctly interpreting physical concepts. Clarity in definitions helps differentiate between how scalars and vectors are utilized in scientific contexts.