WEBC is the third (3rd) letter in the English alphabet and ISO basic latin alphabet. Meanings for C. In temperature, °C means "degrees Celsius ". In music, C is a note sometimes referred to as “Do”. In chemistry, C is the atom of carbon, as in C40 H 56. In physics, c is the speed of light, as in E=mc². In Roman numerals, C means "one hundred " (100).