Pragmatic ambiguity is when a sentance that is unambiguous after sematic analysis may still have different meanings in different contexts, which needs to be resolved during pracgmatic analysis. This may be related to time or location; for example the meaning of "I've been here for three years" depends on where and when it is said – indeed even 'here' may mean the current location or a state of the world, such as being over-tired. There may also be social factors at play, for example is "it's cold in here" simply a statement of fact, a request for you to close the door, or a rebuke for leaving it open in the first place?
Used in Chap. 13: page 190