The definition of Arab countries is:
Arab countries generally refer to countries dominated by the Arab nation. They have a unified language - Arabic, a unified culture and customs, and the vast majority of them believe in Islam. Although some countries are not predominantly Arab, they have long established close political, economic, cultural, and religious ties with Arab countries, and have joined the League of Arab States, so they are also called Arab countries. There are currently 22 Arab countries and regions, with a total area of more than 14 million square kilometers and a total population of about 150 million.
Arab countries are mainly distributed in West Asia and North Africa, including 12 West Asian countries such as Palestine, Jordan, Syria, Lebanon, Saudi Arabia, Iraq, Yemen, Kuwait, United Arab Emirates, Qatar, Bahrain, and Oman; Algeria, Morocco , Tunisia, Libya, Sudan, Mauritania, Egypt and other 7 North African countries; Djibouti and Somalia in eastern Africa and Comoros, an island country in the western Indian Ocean.
Islamic countries are defined as:
“Islamic countries” generally refer to countries and regions where Islam is the state religion and where the majority of residents believe in Islam (Islamic countries are sometimes also called Muslim countries, Muslim means Islamic believer).
In other words, a country that uses Arabic as its official language is an Arab country; a country that uses Islamic law as its law is an Islamic country. All Arab countries are Islamic countries, but not all Islamic countries are necessarily Arab countries.
Extended information:
The Arabs created Islam, and all Arab countries use Islam as their state religion. Therefore, all 23 Arab countries are also Islamic countries (there are also Muslim countries) without exception. But besides the Arabs, there are many countries that believe in Islam as their state religion. This is because the Arab Empire spread Islam to most of the world in the Middle Ages. These countries that use Islam as their state religion are so-called "Islamic countries". Currently, there are 49 Islamic countries, including Arab countries.
Islamic countries refer to countries whose citizens are mainly Islamic believers (Muslims).
Some countries implement a theocracy policy, but most of them are considered to be "theocracy" regimes (family rule is opposed to Islamic law) and they only selectively implement Islamic law based on their political interests. , so Islamic law is limited to civil litigation. Islamic countries are mainly distributed in the Middle East, the Arabian Peninsula, and other regions in Africa and Asia. Such as Iran, Afghanistan, Yemen, Saudi Arabia, Türkiye, Indonesia, etc.
Reference materials: Baidu Encyclopedia-Arab countries? Baidu Encyclopedia-Islamic countries