Ambiguity is the property of words, terms, and concepts, (within a particular context) as being in undefined, undefinable, or otherwise vague, and thus having an unclear meaning. A word, phrase, sentence, or other communication is called "ambiguous" if it can be interpreted in more than one way. Ambiguity is distinct from vagueness, which arises when the boundaries of meaning are indistinct. Ambiguity is in contrast with definition, and typically refers to an unclear choice between standard definitions, as given by a dictionary, or else understood as common knowledge.
Lexical ambiguity arises when context is insufficient to determine the sense of a single word that has more than one meaning. For example, the word "bank" has several meanings, including "financial institution" and "edge of a river", but if someone says "I deposited $100 in the bank", the intended meaning is clear. More problematic are words whose senses express closely related concepts. "Good", for example, can mean "useful" or "functional" (That's a good hammer), "exemplary" (She's a good student), "pleasing" (This is good soup), "moral" (He is a good person), and probably other similar things. "I have a good daughter" isn't clear about which sense is intended. The various ways to apply prefixes and suffixes can also create ambiguity (‘undeletable’ can mean “possible to undelete” or “impossible to delete”).
Syntactic ambiguity arises when a sentence can be parsed in more than one way. "He ate the cookies on the couch", for example, could mean that he ate those cookies which were on the couch (as opposed to those that were on the table), or it could mean that he was sitting on the couch when he ate the cookies. Spoken language can also contain lexical ambiguities, where there is more than one way to break up a set of sounds into words, for example "ice cream" and "I scream". This is rarely a problem due to the use of context.
Philosophers (and other users of logic) spend a lot of time and effort searching for and removing ambiguity in arguments, because it can lead to incorrect conclusions and can be used to deliberately conceal bad arguments. For example, a politician might say "I oppose taxes which hinder economic growth". Some will think he opposes taxes in general because they hinder economic growth; others will think he opposes only those taxes that he believes will hinder economic growth (although in writing, the correct insertion or omission of a comma after "taxes" removes ambiguity here - in addition, for the latter meaning, "that" is properly used in place of "which"). The politician hopes that each will interpret the statement in the way he wants, and both will think the politician is on his side. The logical fallacies of amphiboly and equivocation also rely on the use of ambiguous words and phrases.
In literature and rhetoric, on the other hand, ambiguity can be a useful tool. Groucho Marx's classic joke depends on a grammatical ambiguity for its humor, for example: Last night I shot an elephant in my pajamas. What he was doing in my pajamas I'll never know. Songs and poetry often rely on ambiguous words for artistic effect, as in the song title "Don't It Make My Brown Eyes Blue" (where "blue" can refer to the color, or to sadness).
In music pieces or sections which confound expectations and may be or are interpreted simultaneously in different ways are ambiguous, such as some polytonality, polymeter, other ambiguous meters or rhythms, and ambiguous phrasing, or (Stein 2005, p.79) any aspect of music. The music of Africa is often purposely ambiguous. To quote Sir Donald Francis Tovey (1935, p.195), "Theorists are apt to vex themselves with vain efforts to remove uncertainty just where it has a high aesthetic value."
Some languages have been created with the intention of avoiding ambiguity, especially syntactic ambiguity. Lojban and Loglan are two nearly identical languages which have been created with the intention of being clear and impossible to misunderstand. The languages can be both spoken and written. Their unambiguity makes them better suited than natural languages for use in communication between humans and computers.
In debate, according to Discovering the World through Debate, "ambiguity" is "A fallacy of language that occurs when a word in an argument has two or more possible meanings and the listener has no means to determine adequately which meaning the arguer intends" (246).
Sometimes, multiple theories about a forensic case can constitute ambiguity.
Trapp, Robert, et al. Discovering the World through Debate: A Practical Guide to Educational Debate for Debaters, Coaches, and Judges. Third Edition. New York: IDEA Press Books, 2005.