Answer:
Coordinating conjunctions.
Explanation:
It can replace coordinating conjunctions, such as: "for", "and", "nor", "but", "or", "yet", "so".
Exemplifying this: By and large, I am fond of learning the English language, but it is such a hard nut to crack sometimes.
Paraphrasing this: By and large, I am fond of learning the English language; it is such a hard nut to crack sometimes.
