Arabia → Arab and Muslim.Egypt → Arab and Muslim-majority.Pakistan → Muslim-majority, but not Arab.

The main difference is language/culture vs religion:

Arab World
Muslim World
Based on
Arabic language & Arab culture
Islam / Muslim identity
Includes
Arab countries such as Egypt, Saudi Arabia, Iraq, Morocco
Countries with large Muslim populations worldwide
Examples
Egypt, Saudi Arabia, Morocco, Iraq
Indonesia, Pakistan, India, Turkey, Iran, Bangladesh, etc.
Are all people Muslim?
No
By definition, Muslims are followers of Islam
Simple example
Saudi Arabia → Arab and Muslim.
Egypt → Arab and Muslim-majority.
Pakistan → Muslim-majority, but not Arab.
Indonesia → Muslim-majority, but not Arab.
Iran → Muslim-majority, but not Arab; its main language is Persian.
India → Has one of the world's largest Muslim populations, but India is not an Arab country.
So, “Arab” does not mean “Muslim,” and “Muslim” does not mean “Arab.”
A useful way to remember it: Arab = primarily a linguistic/cultural identity; Muslim = a religious identity.