There are different Usages of the letter T.
1. the twentieth 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 S in a set of items, categories, sizes, etc. e.g. It also denotes the twentieth of twenty or more hypothetical people or things.
t = temperature as the measure of hotness. T = Terra which is also a unit of measurement where 1T = 1012 units as in TB, Terra Bytes. Besides, T letter of the English Alphabet is used in Thailand as the International Vehicle Registration.
In Physics T = Tesla the SI unit of Magnetic Flux Density.
The most Common Noun which is used to learn this letter at the Nursery level is Tap; T for Tap.