ad-Din, is a laqab, a component of some Arabic name

Arabic name

Long ago, Arabic names were based on a long naming system; most Arabs did not simply have given/middle/family names, but a full chain of names. This system was in use throughout the Arab world. Today however, Arabic names are similar in structure to those of Modern and Western names...

s, meaning "of the faith". The names concerned are used by Muslim

Muslim

A Muslim, also spelled Moslem, is an adherent of Islam, a monotheistic, Abrahamic religion based on the Quran, which Muslims consider the verbatim word of God as revealed to prophet Muhammad. "Muslim" is the Arabic term for "submitter" .Muslims believe that God is one and incomparable...

s all over the world.

The meaning of the word "Din", simply translated "faith", is explained further on the Dīn

Dīn

is an Arabic word commonly associated with Islam, but also used in Arab Christian worship. The term is sometimes translated as "religion", but as used in the Qur'an, it refers both to the path along which righteous Muslims travel in order to comply with divine law, or Shari'a, and to the divine...

 page.

The Arabic spelling corresponds to the letters "a l d i n", but because the letter "d" is a sun letter the letter "l" is here assimilated to it, and simply lengthens the sound of the "d". The initial vowel, written here as "a", is unstressed and can be transliterated into almost any vowel in the Latin alphabet. Spacing, hyphenation, the insertion of apostrophes and capitalisation are all variable. Commonly occurring representations are:

• al-Din
• ad-Din
• ad-Dīn
• ud-Din
• -uddin (particularly in English
  English language
  English is a West Germanic language that arose in the Anglo-Saxon kingdoms of England and spread into what was to become south-east Scotland under the influence of the Anglian medieval kingdom of Northumbria...
  
  -speaking south
  South Asia
  South Asia, also known as Southern Asia, is the southern region of the Asian continent, which comprises the sub-Himalayan countries and, for some authorities , also includes the adjoining countries to the west and the east...
  
   and east Asia
  East Asia
  East Asia or Eastern Asia is a subregion of Asia that can be defined in either geographical or cultural terms...
  
  )
• -uddeen (particularly in English-speaking south and east Asia)
• -eddine (particularly in French
  French language
  French is a Romance language spoken as a first language in France, the Romandy region in Switzerland, Wallonia and Brussels in Belgium, Monaco, the regions of Quebec and Acadia in Canada, and by various communities elsewhere. Second-language speakers of French are distributed throughout many parts...
  
  -speaking areas)
• -ettin (particularly in Turkish name
  Turkish name
  A Turkish name consists of an ad and a soyadı . Turkish names exist in a "full name" format. While there is only one soyadı in the full name, there may be more than one ad...
  
  s)

There are disambiguation pages for many of the names concerned, such as:

Ala-ud-din Ala-ud-din Aladdin is a male given name which means "nobility of faith" or "nobility of religion". It is one of a large class of names ending with ad-Din... Alimuddin Amin ud-Din Anwaruddin Azharuddin Azim ud-Din Badr al-Din Baha' al-Din Burhan al-Din Fakhr al-Din Fariduddin Ghiyath al-Din Hamid al-Din Haqq ad-Din Hisham ud-Din Husam ad-Din Ikhtiyar al-Din Imad al-Din Ismat ad-Din

Izz al-Din Jalal ad-Din Jamal ad-Din Kamal al-Din Kamal al-Din Kamal al-Din is a male Muslim given name formed from the elements Kamal and ad-Din, meaning perfection of religion. It may refer to:*Kamal al-Din Ibn al-Adim , Arab historian... Khair ad-Din Majd ad-Din Mansur ad-Din Mohy al-Din Moinuddin Muhib ud-Din Mu'iz ad-Din Muslih ud-Din Najm al-Din Nasir al-Din Nazimuddin Nizam al-Din Nur al-Din Qamar ud-Din Qutb ad-Din

Rashid al-Din Riazuddin Rukn al-Din Sabr ad-Din Sa'd al-Din Sadr al-Din Safi al-Din Saif al-Din Ṣalāḥ ad-Dīn Shams al-Din Sharaf al-Din Shihab al-Din Shujauddin Sirajuddin Taj al-Din Taqi al-Din Zahir al-Din Zayn ad-Din Ziauddin

Use as separate surname

In modern times in English-speaking environments the name Uddin has sometimes been used as if it was a separate surname. Some examples are:

• Pola Uddin, Baroness Uddin
  Pola Uddin, Baroness Uddin
  Manzila Pola Uddin, Baroness Uddin is a British Labour politician, and community activist.-Background:Uddin was born in a village in Bangladesh. She moved with her parents to the United Kingdom in 1973, when she was 13 years of age, and she grew up in the East End of London...
  
   (born 1959), British politician
• Keith Uddin
  Keith Uddin
  Keith Uddin , also known as KU, is a songwriter and record producer/engineer.Keith Uddin has had 78 consecutive top 20 singles & albums, as a producer/engineer and/or writer, worldwide, so far this Century, and 42 of those singles and albums went to No1...
  
  (born 1979), British songwriter