Meaning:
“老” means “old,” and “铁” means “iron.” Originating from a northeastern Chinese dialect, this term can be used as an adjective referring to “unbreakable” friendships, alluding to the metal that is strong and tough. It is also used as a noun meaning “bosom buddies.” When used on a man and a woman, sometimes the term can imply that they have a secret relationship. However, after the term was picked up by netizens across China, it’s most often used simply to mean “very close friends.”
Example:
A: 有件快递我帮你拿上来了，好像是什么吃的。
Yǒu jiàn kuàidì wǒ bāng nǐ ná shànglái le, hǎoxiàng shì shénme chī de。
I picked up your parcel from the delivery guy downstairs. It looks like some food.
B: 是一箱蓝莓，我小学同学从家乡寄来的。
Shì yīxiāng lánméi, wǒ xiǎoxué tóngxué cóng jiāxiāng jì lái de。
That’s a box of blueberries my primary school classmate sent me from my hometown.
A: 小学同学还有联系，真不容易。
Xiǎoxué tóngxué hái yǒu liánxì, zhēn bù róngyì。
It’s not easy that you guys have kept in touch since primary school.
B: 他是我一辈子的老铁。
Tā shì wǒ yībèizi de lǎotiě。
He’s my best friend for life.
(First editor: Debra Li)