A “god” usually refers to a powerful entity that creates or controls events, things, and other beings. Many religions include a god or gods.
Monotheistic (“one god”) religions claim there is only one god who is the creator of the universe. In English, this god is named God with a capital letter.
In Islam, God is called Allah. Allah also has many other names describing different ways in which he is perfect.
In Judaism, G-d’s names are considered sacred. There are many rules about speaking and writing the names.
Text adapted from Simple English Wikipedia, Creative Commons Attribution-ShareAlike License 4.0.
Illustration from Cosmographia (Münster) 16th or 17th century via Wikimedia Commons, Public Domain