Who's is a contraction of the words "who" and "is." It is important to note that the apostrophe in "who's" represents the missing letter "i" in "is." Some synonyms for "who's" include "who is," "who has," and "who'd." "Who is" is typically used to inquire about the identity of a person or group, while "who has" is commonly used to refer to possession or ownership. "Who'd" is short for "who would" and is often used in hypothetical or conditional statements. It is important to use these synonyms appropriately in different contexts to ensure clear communication.