Description: The 'Expression of the Day' series featured in this book began in 2014, about four years after I started my free English education channel, 'English in Korean.' The goal was to focus on teaching the expressions that Korean learners were most curious about. Over the following years, I created dozens of lessons, and this year, as the series reached its 100th episode, I decided to compile the content into this book. You can watch video lessons covering all the expressions on YouTube, and beyond the example sentences shown in the videos, I've added detailed explanations, dialogues, and synonyms to make the content even more complete. In addition to this series, I run a free English learning podcast (the EnglishinKorean Podcast), YouTube channels with over 500 lessons (English in Korean and English in Korean Plus!), and a free English learning website (http://www.EnglishinKorean.com) — all to help Korean learners study English at no cost. With the free English learning resources I provide online, you could listen to a different lesson every day for several years without running out of content. I truly hope this book and these resources can be helpful to many people in their English learning journey!