In this lesson, students will learn to identify definition signal words such as 'is', 'called', 'or', and the use of commas to define new vocabulary terms. Through examples related to ichthyology and deep-sea creatures, students will explore how these signals clarify meanings, while also understanding that other words like 'but' and 'however' indicate contrast rather than definition. The lesson culminates with a writing exercise where students create their own sentences about the deep sea using the defined signal words.