| Term | Definition | | Quantum | A quantum is the smallest indivisible unit of energy. |
| Quarantine | A way to prevent the spread of disease by isolating a person or animal who has not been diagnosed with a communicable disease but who was exposed or is likely to have been exposed to that disease. |
| Radiation | Energy transfer in the form of electromagnetic waves or particles that release energy when absorbed by an object. |
| Randomized Trial | A study where participants are randomly assigned into either the intervention group or the control group. This is done to prevent bias among researchers, who may be subconsciously wishing for the study to show a particular result. |
| Recombinant | Of or resulting from new combinations of genetic material or cells; the genetic material produced when segments of DNA from different sources are joined to produce recombinant DNA. |
| Reflectivity | The ability of a surface material to reflect sunlight including the visible, infrared, and ultraviolet wavelengths. |
| Reforestation | Planting of forests on lands that have previously contained forests but that have been converted to some other use. |
| Reinforcement learning | Reinforcement learning is a process where a model learns to be more accurate by having its outputs assessed, either by a human or by another AI designed to rank them. |
| Respiration | The process whereby living organisms convert organic matter to CO2, releasing energy and consuming O2. |
| Review Article | A scientific article that compiles past research on one topic to analyze trends and assess the current state of knowledge on that topic. |
