A physical property characterizing some aspect of Nature that can be measured.
Examples: time, speed, energy
SYMBOL:
Visible structure used to identify or tag the physical quantity.
Examples:t, v, E
NUMBER:
The numerical value associated with a measurement of a physical quantity. This number represents the value of the state of the quantity at some moment or location.
Examples: 10.3 s, 140 m/s, 84.1 kJ
UNITS:
The numerical value of some physical quantity is incomplete without a reference to the "size" of the numbers. A value's units state the standard to which the number will be compared.