Ternary (from Latin ternarius) or trinary is an adjective meaning "composed of three items". It can refer to:

• Ternary numeral system, a base-3 counting system
  • Balanced ternary, a positional numeral system, useful for comparison logic
• Ternary logic, a logic system with the values true, false, and some other value
• Ternary plot or ternary graph, a plot that shows the ratios of three proportions
• Ternary relation, a finitary relation in which the number of places in the relation is three
• Ternary operation, an operation that takes three parameters
• Ternary function, a function that takes three arguments

• Ternary signal, a signal that can assume three significant values
• Ternary computer, a computer using a ternary numeral system
• Ternary tree, a tree data structure in computer science
  • Ternary search tree, a ternary (three-way) tree data structure of strings
• Ternary search, a computer science technique for finding the minimum or maximum of a function
• Ternary heap, a data structure in computer science
• Ternary Golay code, a perfect [11, 6, 5] ternary linear code
• ?:, a ternary conditional operator used for basic conditional expressions in several programming languages

• Ternary complex, a complex formed by the interaction of three molecules
• Ternary compound, a type of chemical compound
• Ternary form, a form used for structuring music
• Ternary name for any taxon below the rank of species

• Tertiary (disambiguation)
• Binary (disambiguation)
• Quaternary (disambiguation)