The "100 series" refers to a classification system used in various fields, including library science and education. In libraries, it often denotes the first section of the Dewey Decimal Classification, which organizes books by subject. The 100s typically cover topics related to philosophy and psychology, providing a framework for categorizing literature in these areas. In the context of education, the "100 series" can also refer to introductory courses at colleges and universities, such as Psychology 101 or Philosophy 100. These courses are designed to provide foundational knowledge and skills, making them accessible to students new to the subject matter.