"Unambiguity" is a measurement of how sure the other players can be of their letters. It's the sum of each player's unambiguity, which for each player is calculated as 1/N where N is the number of possible letters their letter could be.
For example, if a player is looking at the clue "_lue", their possibilities are b,c,f,g. 4 possibilities gives an unambiguity of 0.25 (1/4) for that player. If this were in a 3p game and the other player was looking at c_ue, they have only l as a possibility for an unambiguity of 1/1 = 1. The total unambiguity of the clue is 0.25 + 1 = 1.25.
The clue you typed is assumed to be a valid word for this calculation.
When there are duplicate letters for the clue-giver to choose from, all possible sequences of letters are considered when calculating unambiguity. Only the best possible score is shown here.
You can see each possible letter for your clue by clicking on the other players' letters.
Score is found by starting with the Unambiguity, adding 0.1 for each non-player letter used, then subtracting 0.25 if the wild was used.