Association; company; friendship — social relations or companionship. As 交際する, it often means to associate or keep company.
大学に入ってから交際の輪が広がった。
My circle of acquaintances expanded after entering university.
仕事上の交際はほどほどにして、無理な付き合いは断るべきだ。
Keep business socializing moderate; you should decline relationships you can't manage.
彼とは長い交際があり、信頼している。
I've had a long association with him and trust him.
(Romantic) involvement; dating — referring to a romantic relationship (as in 交際する = to date someone).
彼女と交際して半年になる。週末はよく一緒に出かける。
I've been dating her for six months. We often go out together on weekends.
親は子供の交際を心配しているが、本人たちは真剣だ。
The parents worry about their child's dating, but the couple are serious.
交際相手を紹介したら、家族は好印象だった。
When I introduced my partner, the family had a good impression.