Cognomen ไส้ (Sai 
, ไส้, Fillingam) , all over the world, is a widespread last name. The last name ไส้ is characteristic of Mongolia, where it is a prevalent surname, Myanmar, where it is a common surname, and Malaysia, where it is quite a common surname (explore the name in all countries). Not in comparison with a country's population, this name is the most popular in Myanmar, India, and Mongolia. More prevalently, ไส้ is the forename as well as the last name.