China 
Africa 
- Clinching
- Clinical chemistry
- Clinical decision support system
- Clinical dementia rating
- Clinical pathology
- Clinical pathway
- Clinical trials
- Clinker
- Clinoptilolite
- Clipboard
- Clipping
- Clique
- Clique graph
- Clique problem
- Cloak of invisibility
- Cloaking devices
- Clock
- Clock drift
- Clock gating
- Clock generator
- Clock rate
- Clock recovery
- Clock signal
- Clock skew
- Clock synchronization
- Clock towers
- Clofazimine
- Clofibric acid
- Clojure
- Clonal selection
- Clonal selection algorithm
- Clone
- Cloning
- Cloning vectors
- Clopen
- Clopyralid
- Close
- Closed
- Closed convex function
- Closed head injury
- Closed systems
- Closed-cycle gas turbine
- Closed-form expression
- Closed-head injury
- Closed-loop
- Closed-loop control
- Closed-loop controller
- Closed-loop manufacturing
- Closed-loop pole
- Closed-loop recycling
- Closed-loop transfer function
- Closeness
- Closeness centrality
- Clostridia
- Clostridiaceae
- Clostridium acetobutylicum
- Clostridium autoethanogenum
- Clostridium beijerinckii
- Clostridium botulinum
- Clostridium difficile
- Clostridium ljungdahlii
- Clostridium pasteurianum
- Clostridium perfringens
- Clostridium saccharobutylicum
- Clostridium sporogenes
- Clostridium tetani
- Clostridium thermocellum
- Closure
- Closure operator
- Closure phase
- Cloth face mask
- Cloth filters
- Cloth modeling
- Cloth of gold
- Clothes dryer
- Clothianidin
- Clothing industry
- Clothtech
- Cloud
- Cloud chamber
- Cloud computing
- Cloud computing architecture
- Cloud computing security
- Cloud condensation nuclei
- Cloud database
- Cloud manufacturing
- Cloud point
- Cloud radiative forcing
- Cloud robotics
- Cloud security
- Cloud seeding
- Cloud storage
- Cloud storage service
- Cloud-native
- CloudCompare
- Cloudant
- Cloudlet
- Clover
- Clozapine
- Cls
- Cluster analysis
- Cluster graph
- Cluster headaches
- Cluster manager
- Cluster of differentiation
- Cluster sampling
- Clustering coefficient
- Clusters
- Clutch
- Clutter
- Cmh2o
- Cnoidal waves
- Co-adaptation
- Co-carcinogen
- Co-channel interference
- Co-energy
- Co-fermentation
- Co-fired ceramic
- Co-firing
- Co-location
- Co-occurrence networks
- Co-oximeter
- Co-processing
- Co-receptor
- Co-simulation
- Co-stimulation
- Co-training
- Co3O4
- CoAP
- Coacervates
- Coactivators
- Coagulase
- Coagulation
- Coagulopathy
- Coal
- Coal analysis
- Coal basin
- Coal blending
- Coal combustion products
- Coal combustion residuals
- Coal dust
- Coal gas
- Coal gasification
- Coal measures
- Coal mining
- Coal oil
- Coal phase-out
- Coal preparation plant
- Coal refuse
- Coal slurry