"That Is" is a phrase commonly used in English to clarify or specify something. It often introduces an explanation or definition, helping to provide more context to a statement. For example, when someone says, "I enjoy outdoor activities; that is, hiking and biking," they are elaborating on what they mean by outdoor activities. In written and spoken communication, "that is" can also be abbreviated as "i.e.," which stands for the Latin phrase "id est." This abbreviation serves the same purpose of clarification. Using "that is" or "i.e." can enhance understanding by ensuring the audience knows exactly what is being referred to in a conversation or text.