The letter G was created in the third century BC by Spurius Carvilius Ruga. At the time, the letter C sounded like the "c" in "cat" and the "g" in "girl". To make the difference more clear, Ruga created the letter G.
Letter G stands for GPRS (General Packet Radio Service). It indicates the slowest speed of Internet data transfer in your mobile phone. When you see G near your signal strength indicator, it is certain that your net connection is working at the slowest speed. 2G, 3G and 4G indicates different speed of internet.
In particle physics, lowercase G stands for the gluon.
In particle physics, the uppercase G stands for the not yet discovered Graviton. There are two sounds of the letter G, hard and soft. If you have an L after it, you have glad. You have grandmother if R is after it, too. Some words start with a silent G before N, such as gnat and gnome. The silent G coming before N can also come at the end of other words, such as in the word sign.
The dictionary definition of g at Wiktionary Media related to G at Wikimedia Commons