Mitochondria are often referred to as the "powerhouses" of the cell because they generate adenosine triphosphate (ATP), the primary energy currency of cells, through the process of oxidative phosphorylation. They also play crucial roles in regulating cellular metabolism, apoptosis (programmed cell death), and calcium homeostasis. Additionally, mitochondria are involved in generating reactive oxygen species (ROS) and play a role in signaling pathways that affect cellular function and health.