Sluicing is a linguistic phenomenon where a part of a sentence is omitted, typically a wh-phrase, while still allowing the meaning to be understood. For example, in the sentence "I know who is coming, but I don't know who," the second "who" is omitted, yet the listener can infer the missing information. This construction often occurs in questions and can help streamline communication. Sluicing is commonly studied in the field of syntax, which examines sentence structure, and is relevant in understanding how language can convey meaning efficiently without unnecessary repetition.