There are different Usages of the letter Z.
1. the twenty-sixth letter of the English alphabet
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
This letter denotes the next after Y in a set of items, categories, sizes, etc. e.g. It also denotes the twenty-sixth of twenty six or more hypothetical people or things.
Z = Atomic Number Besides, Z letter of the English Alphabet is used in Zambia as the International Vehicle Registration.
In Chemistry Z = Atomic Number.
The most Common Noun which is used to learn this letter at the Nursery level is Zebra; Z for Zebra.