Z is the 26th and final letter in the modern alphabet. It is pronounced zed in UK (sometimes zad) and zee in USA. Its older English name was izzard.
Z stems from the Greek zeta which originates from zayin, the seventh letter in the Semitic alphabet.
In mathematics z is the third unknown quantity in an algebraic expression. Descartes introduced x, y and z as symbols for unknown quantities in 1637.
In mediaeval times z was the symbol for 2000.