| Compound | (Environmental Engineering) A substance composed of two or more elements. |
| Compression settling | (Environmental Engineering) Settling which occurs in the lower reaches of clarifiers where particle concentrations are highest. Particles can settle only by compressing the mass of particles below. |
| Consumers | (Environmental Engineering) Organisms which consume protoplasm produced from photosynthesis or consume organisms from higher levels which indirectly consume protoplasm from photosynthesis. |
| Conversion | (Environmental Engineering) The fraction of a species entering a system which is converted to product. |
| Corrosive waste | (Environmental Engineering) A waste that is outside the pH range of 2 to 12.5 or a waste that corrodes steel at a rate greater than 6.35 mm (0.25 in) per year. One of EPA's four hazardous waste properties. |
| Covalent bond | (Environmental Engineering) A bond in which electrons are shared approximately equally by two atoms. |
| Cybernetic | (Environmental Engineering) Systems which change in response to feedback. |
| CASE - | (Software Engineering) Computer-aided software engineering, see also, Tools |
| Cause-effect graphing - | (Software Engineering) a black-box testing method |
| Change control - | (Software Engineering) an umbrella process that enables a project team to accept, evaluate, and act on changes in a systematic manner |