Explanation:

Present Perfect Continuous Tense:
- The sentence "Her grandma has been talking for three hours" uses the present perfect continuous tense.
- This tense is used to indicate an action that started in the past, continued up to the present moment, and may still be ongoing.
- In this case, it means that her grandma started talking in the past, has been talking continuously, and is likely still talking at the time of speaking.

Use of "Has been talking":
- The verb "talk" is in the present perfect continuous form "has been talking" in this sentence.
- The auxiliary verb "has been" indicates that the action of talking started in the past and has continued up to the present moment.
- The word "talking" is the present participle form of the verb "talk," used in continuous tenses.

Duration of the Action:
- The phrase "for three hours" specifies the duration of the action.
- It tells us that her grandma has been talking continuously for the past three hours without stopping.

Overall Meaning:
- Putting it all together, the sentence conveys the idea that her grandma started talking in the past, has been talking continuously for the past three hours, and is likely still talking at the time of speaking.