in biology, an organ system is a biological system consisting of a group of organs that work together to perform functions
organs are between organs and organisms in biological organization

here is a table of organ systems in humans

descriptioncomponent organs
respiratory systembreathing: exchange of oxygen and carbon dioxidenose, mouth, paranasal sinuses, pharynx, larynx, trachea, bronchi, lungs and thoracic diaphragm
digestive system and excretory systemdigestion: breakdown and absorption of nutrients, excretion of solid wastesteeth, tongue, salivary glands, esophagus, stomach, liver, gallbladder, pancreas, small intestine, large intestine, rectum and anus
circulatory systemcirculate blood in order to transport nutrients, waste, hormones, O2, CO2, and aid in maintaining pH and temperatureblood, heart, arteries, veins and capillaries
urinary systemmaintain fluid and electrolyte balance, purify blood and excrete liquid waste (urine)kidneys, ureters, bladder and urethra
integumentary systemexterior protection of body and thermal regulationskin, hair, fat and nails
skeletal systemstructural support and protection, production of blood cellsbones, cartilage, ligaments and tendons
muscular systemmovement of body, production of heatskeletal muscles, smooth muscles and cardiac muscle
endocrine systemcommunication within the body using hormones made by endocrine glandshypothalamus, pituitary, pineal gland, thyroid, parathyroid and adrenal glands, ovaries and testicles
exocrine systemvarious functions including lubrication and protectionceruminous glands, lacrimal glands, sebaceous glands and mucus
lymphatic systemreturn lymph to the bloodstream, aid immune responses, form white blood cellslymph, lymph nodes, lymph vessels, tonsils, spleen and thymus
nervous systemsensing and processing information, controlling body activitiesbrain, spinal cord, nerves, sensory organs and the following sensory systems (nervous subsystems): visual system, olfactory system, taste (gustatory system) and hearing (auditory system)
reproductive systemsex organs involved in reproductionovaries, fallopian tubes, uterus, vagina, vulva, penis, testicles, vasa deferentia, seminal vesicles and prostate

additionally, the immune system is a network of biological systems that protects an organism from diseases