In orthography, the phonemic principle holds that there should be a one-to-one correspondence between the orthographic and phonemic representation of a word, or more strictly, that there should be a one-to-one correspondence between graphemes and phonemes (which requires the writing system in question to be an alphabet or an abugida). Usually it is however not required for prosodic features like stress and tone to be unambiguously marked.
Languages whose orthographies are very nearly phonemic include Spanish and Finnish. Such writing is often called "phonetic", but this is incorrect, as predictable allophonic variations, eg. [d ~ ð] in the former or [h ~ x] in the latter, are usually not overtly marked.