China 
Africa 
- Decidability
- Decidable
- Decidua
- Decidualization
- Decile
- Decimal
- Decimal degrees
- Decimal point
- Decimal representation
- Decimal time
- Decimeters
- Decision aids
- Decision analysis
- Decision boundary
- Decision fatigue
- Decision matrix
- Decision model
- Decision problems
- Decision quality
- Decision support system
- Decision table
- Decision theory
- Decision trees
- Decision-making
- Decision-making software
- Decision-matrix method
- Deck
- Declaration
- Declaration of the Independence of Cyberspace
- Declarative
- Declarative programming
- Declination
- Decline curve analysis
- Decoction
- Decoherence
- Decommissioning
- Decompiler
- Decomposed granite
- Decomposition method
- Decompression
- Decompression sickness
- Decompressive craniectomy
- Deconditioning
- Deconstruction
- Deconvolution
- Decorin
- Decorrelation
- Decoupling capacitor
- Decoy receptors
- Dedekind cuts
- Dedekind-complete
- Dedifferentiation
- Deduction theorem
- Deductive database
- Deductive reasoning
- Deep brain stimulation
- Deep drawing
- Deep eutectic solvent
- Deep fascia
- Deep foundation
- Deep geological repository
- Deep learning
- Deep ocean water
- Deep reinforcement learning
- Deep sea mining
- Deep space exploration
- Deep space network
- Deep time
- Deep underground
- Deep vein
- Deep-cycle batteries
- Deep-cycle battery
- DeepFace
- Deepfakes
- Deepwater drilling
- Default
- Default logic
- Default passwords
- Defected ground structure
- Defective
- Defective matrix
- Defective pixel
- Defects
- Defence in depth
- Defense in depth
- Defensins
- Defensive programming
- Defibrator
- Defibrillation
- Defibrillators
- Deficiency
- Deficit irrigation
- Definite matrix
- Definition
- Deflagration
- Deflagration to detonation transition
- Deflate
- Deflection
- Deflection yoke
- Defluoridation
- Defoamer
- Defocus aberration
- Defoliants
- Deforestation
- Deformable mirror
- Deformation
- Deformation mechanisms
- Deformation monitoring
- Deformation theory
- Defrosting
- Defuzzification
- Degassed water
- Degassing
- Degeneracy
- Degenerate
- Degenerate distribution
- Degenerate semiconductor
- Degeneration
- Degenerative disc disease
- Deglaciation
- Degradation
- Degranulation
- Degreasers
- Degree distribution
- Degree matrix
- Degree of a polynomial
- Degree of belief
- Degree of coherence
- Degree of curvature
- Degree of frost
- Degree of parallelism
- Degree of polymerization
- Degree of reaction
- Degree of truth
- Degrees
- Degrees of freedom
- Dehalogenation
- Dehiscence
- Dehumidifier
- Dehydration
- Dehydration reaction
- Dehydroascorbic acid
- Dehydroepiandrosterone
- Dehydrogenase
- Dehydrogenation
- Dehydrohalogenation
- Deicing
- Deinking
- Deinococcus radiodurans
- Deiodinase