The basic and literal meaning of 出轨 chū guǐ is: be derailed; go off the rails; jump the rails. It has two figurative meanings:
1. overstep the bounds (language and behavior are out of principle or beyond the limits). 2. have an extramarital affair
Examples:
出轨, be derailed; go off the rails; jump the rails
火车出轨时, 数百人受伤。huǒ chē chū guǐ shí , shù bǎi rén shòu shāng。
Hundreds of people were injured when the train went off the rails.
这列由１８节车厢组成的列车，有１４节出轨倾翻，其中一节落入河中。zhè liè yóu １８jiē chē xiāng zǔ chéng de liè chē ，yǒu １４jiē chū guǐ qīng fān ，qí zhōng yī jiē luò rù hé zhōng 。
The train consisted of 18 coaches, of which 14 derailed and toppled, with 1 fell into the river.
你知道吗，我刚听说火车昨晚出轨了。nǐ zhī dào ma ，wǒ gāng tīng shuō huǒ chē zuó wǎn chū guǐ le 。
Do you know, I have just been told that the train got derailed last night.
出轨, overstep the bounds
他们用未成年酗酒狂欢和其他的出轨行为来表达对不负责任的父亲的愤恨。tā men yòng wèi chéng nián xù jiǔ kuáng huān hé qí tā de chū guǐ háng wéi lái biǎo dá duì bú fù zé rèn de fù qīn de fèn hèn 。
They acted out their resentment at their irresponsible father with underage drinking binges and other escapades.
对女士讲这样的话太出轨了。duì nǚ shì jiǎng zhè yàng de huà tài chū guǐ le 。
It is overstepping the mark to say that to a lady.
出轨, have an extramarital affair
如果他出轨了，就是你离开的时候了。rú guǒ tā chū guǐ le ，jiù shì nǐ lí kāi de shí hòu le 。
If he has cheated on you, it‘s time to move on.
现在官方将婚姻记录放在了网上，这样爱人和配偶可以查找出轨者。xiàn zài guān fāng jiāng hūn yīn jì lù fàng zài le wǎng shàng ，zhè yàng ài rén hé pèi ǒu kě yǐ chá zhǎo chū guǐ zhě 。
Now officials are putting marriage records online so lovers and spouses can check for cheaters.
男人出轨并不是因为他只是不小心被另一个女人的邪恶魅力迷了心窍。nán rén chū guǐ bìng bú shì yīn wéi tā zhī shì bú xiǎo xīn bèi lìng yī gè nǚ rén de xié è mèi lì mí le xīn qiào 。
When a man cheats it‘s not because he was innocently seduced by another woman‘s wicked charms.