The collection of all even integers is a well-defined collection because there couldn’t be difference between choosing the even integers from the collection of given numbers or all the numbers taken at a large. The choice will not vary from person to person. The given collection has well-defined objects which meet the universal criteria.

Hence, this collection is a set.

{x:x=….-6,-4,-2, 0,2, 4, 6…where n is even integer 2k for some unique interger k}