The letter 'j' is the tenth letter of the English alphabet. It represents a voiced palatal approximant sound, often pronounced like the 'j' in "jam." In mathematics, 'j' is often used to denote the imaginary unit in electrical engineering, equivalent to the square root of -1.
The letter 'j' originated from the Latin letter 'I,' which was used as both a vowel and a consonant. Over time, a differentiation was made, and the tail on the 'j' developed in the Middle Ages to distinguish it as a consonant.