Dynamic equivalence and formal equivalence, in translating, is the dichotomy between transparency and fidelity – respectively, between the meaning and the literal structure of a source text.
The dynamic– versus formal-equivalence dichotomy was originally proposed by Eugene Nida in relation to Bible translation.
Translation is the communication of the meaning of a source-language text by means of an equivalent target-language text. The English language draws a terminological distinction (which does not exist in every language) between translating (a written text) and interpreting (oral or signed communication between users of different languages); under this distinction, translation can begin only after the appearance of writing within a language community.
A translator always risks inadvertently introducing source-language words, grammar, or syntax into the target-language rendering. On the other hand, such "spill-overs" have sometimes imported useful source-language calques and loanwords that have enriched target languages.