A qualifier is a word or phrase that limits, modifies, or restricts the meaning of an adjective, verb, or other words in a sentence. It can be used to provide more information about something, such as its size, color, shape, origin, etc., and can also be used to express doubt, uncertainty, or negation. For example, "the tall man" is a simple description, but adding a qualifier like "really tall" provides additional information that the man is above average in height. Similarly, using words such as "probably," "possibly," or "maybe" can indicate a degree of uncertainty about something.