A ambiguous move (or sequence or exchange) or, in a CGT context, an ambiguous option is one that falls between sente and gote. Since “sente” and “gote” are used in practical and theoretical senses, the same applies to “ambiguous”.
The term “sote” has been proposed by Robert Pauli as a synonym, appears in a number of articles on Sensei’s Library and links here; as of writing this usage is probably restricted to this site.
In a practical sense, a move is ambiguous if the opponent can equally well answer it or ignore it. Note that, unlike the theoretical sense, this depends on the whole board.
As an example, suppose the only plays left on the board are a double gote, and another position in which Black can play, threatening a follow-up. If the value of Black’s threat exactly matches that of the gote, his play is practically ambiguous, and White may answer or ignore it as she likes.
In a theoretical sense, a move is ambiguous if it does not change the local temperature. It is therefore neither exactly sente nor gote, since
- sente raises the local temperature, creating the privilege of forestalling the reverse sente, while
- gote lowers it, creating the possibility of tedomari.
Note that this only depends on the local situation.
Relation to ambiguous position
If an ambiguous move (or sequence) is among the largest options of a position, that position is an ambiguous position. But since that term also covers positions with equally good sente and gote options, it is less specific. Use the more specific term “ambiguous move” (as a link to this article) if that is what you mean. “Ambiguous” is ambiguous!
 This is explained by Bill in the article Double Sente Is Relative/ Discussion.
 This is the situation used by Bill in his example in note.