The letter "j" is the tenth letter of the English alphabet. It is a consonant and is often pronounced as /dʒ/, similar to the sound in the words jump and jungle. In the English language, "j" can also represent the sound /j/ in some words, like yes. In mathematics, "j" is commonly used to represent the imaginary unit, which is the square root of -1. This concept is essential in complex numbers, where it helps in solving equations that do not have real solutions. The use of "j" in this context is particularly prevalent in electrical engineering and signal processing.