Final answer:
Conscientiousness refers to a person's organization, dependability, and goal-directed behavior, aligning with the characteristics of being responsible and self-disciplined.
Step-by-step explanation:
The characteristic of being responsible and self-disciplined is best described as conscientiousness. Conscientiousness is one of the Big Five personality traits and refers to a person's level of organization, dependability, and achievement striving, all of which align with being responsible and self-disciplined. Individuals with high conscientiousness tend to be efficient, methodical, and mindful of details, making it the most fitting answer for this description.