Hello Vic, "甲, 乙" are followed by 8 others making a sum of 10 as follows: 甲, 乙, 丙, 丁, 戊, 己, 庚, 辛, 壬, 癸 They are pronounced as : jia, yi, bing, ding, wu, ji, geng, xin, ren, and gui; They are called 是天干 (shitiangan) ,which means literally the 10 heavenly stems. They are used cyclically in the calender constituting the counting system in the Chinese calender. They are also used as ordinal numbers like the Roman I, II, III . They do have so many applications in Chinese Astrology ( calender ) , Feng shui , Chinese herbal medicine and Acupuncture. Otherwise you will rarely use them in daily speech or any written context.

In formal sitautions, like sigining a contrast: 甲方、乙方 or movie cast list, when it comes to some unimportant roles, 路人甲、路人乙etc Do you really often see such words? I think nowadays Chinese people are using English letters more often than 甲、乙、丙 For example, office buildings: Tower A, Tower B; metro exits, exit A, exit B; things like that.

As a Chinese, I think nowadays the most common use is '甲方'，‘乙方’，which means 'this one(person), that one(person)'. They are used in a contract or legal documents to refer to the people involved. You can consider 甲, 乙, 丙, 丁 numbers to express grade, level. For instant, He got '甲等' in the test. This means he got an 'A' . His brother got '乙等'. It refers 'B'. The same goes for 丙, 丁. ‘戊, 己, 庚, 辛, 壬, 癸’ are not used in the way I mentioned. As my limited English, I can't express what is '方' and '等'.

Hi,Vic... 甲jia3 乙yi3 They have been used as numbers... 甲：means "the first one" 乙：means "the second one" there are also some words like "丙、丁..."(the third one..the fourth one...) sometimes...they shows in the pacts..as contracting parties... like.."甲方","乙方“。。。 hope it's helpful..