"Active learning" means students can engage with the material, participate in the class, and collaborate with each other. Don't expect your students simply to listen, take notes and memorize; instead, have them participate and engage with the content to demonstrate a process, model an idea, analyze an argument, or apply a concept to a real-world situation.
Active learning comes in many shapes and forms and is very inexpensive and easy to implement in higher education. Active learning engages students in activities that help them to figure out concepts and collaborate while doing so, thereby building communication and teamwork skills. It also helps everybody in the class to participate meaningfully in their own learning and drives innovation. Some of the active learning that I do in my various classes are having students build play doh models, use sidewalk chalk to go outside and draw and review/explain concepts, work on individual and group projects (project-based learning), have them solve case studies, design and present posters, create videos and TED talks, create podcasts, role-play, act out a science concept through a play and many other activities. I will be blogging about those in the days to come, hopefully one blog per day during summer break. Using different activities in class is technically termed as using 'multiple modalities' of teaching which as the research in the field indicates is helpful for keeping students engaged. The photograph below shows students assembling karyotypes (arranging chromosomes in order from larger to smaller) using a magnetic karyotyping kit in the classroom.