Within the realm of plant biology, a sophisticated and intricate antioxidative system (AOS) exists to combat detrimental reactive species (RS), with a primary focus on reactive oxygen species (ROS). This intricate network functions to preserve cellular homeostasis. Originally, reactive oxygen species (ROS) were identified as harmful byproducts of aerobic metabolic processes. It is a review paper that descries ROS in brief along with its production, source, reactivity, functions and many more. At first it describes about peroxisomes that helps in production of H2O2 & O2- & Production of ROS in vivo & in vitro. Secondly it describes about its Source or origin i.e. from Mitochondria, Transition Metal Ions, ER etc and it also describes about its chemical properties & reactivity of different ROS i.e. H2O2, HO● , O2●- & HO2● in different ways including Haber- Weiss Reaction which are mentioned in details . We also report about the role of ROS in germination process and its functions. To conclude we have reviewed ROS and compiled in a manner which will altogether shed a new light on the roles of ROS in a plant species.