A political party — an organization of people sharing common policies or ideology.
新しい政党が次の選挙に立候補することを発表した。
A new political party announced it will run in the next election.
彼は党の代表に選ばれた。
He was chosen as the party leader.
与党と野党の間で議論が続いている。
Debates continue between the ruling party and the opposition.
Used as a suffix to indicate someone fond of something or a fan of a category (e.g. 甘党 = someone who likes sweets).
彼は甘党で、食後には必ずデザートを食べる。
He's a sweets person; he always eats dessert after meals.
辛党の友達と外食に行くと、いつも辛い物を選ぶ。
When I go out to eat with my spicy-food-loving friend, he always chooses spicy dishes.