Hello, Anee. This is a good question. To know what is "己丑", we should learn about "天干地支" at first. In ancient Chinese, nobody knows common era. However, we have our own chronology. 天干：甲、乙、丙、丁、戊、己、庚、辛、壬、癸（a total of ten） 地支：子、丑、寅、卯、辰、巳、午、未、申、酉、戌、亥 (a total of twelve) Chinese people arrange them together like 甲子、乙丑、丙寅、丁卯、戊辰、己巳、庚午、辛未、壬申、癸酉 and then we go 甲戌 and 乙亥.... Because 天干 has ten charactors and 地支 has twelve charactors, we can get sixty combinations. So you see, we can use them to name the year——今年是农历己丑年. Likewise, 天干地支 can also be used to name months, days and hours. 十二生肖, 也叫做属相，is evolved from the 地支. 子-鼠 丑-牛 寅-虎 卯-兔 ... 十二生肖可用于表示某个人的出生年份。 例如，小明出生于1998年，是农历戊寅年。因此，我们可以说： "小明属虎". 2020年是庚子年，也是鼠年。如果一个人属鼠，那么他今年一定是0岁、12岁、24岁、36岁…… 如果你不好意思问一个人的年龄，你可以试着问他的属相，这样你就知道他多少岁了。

Thanks so much

"己丑" is a name of a year in Chinese calendar system。"天干"：甲、乙、丙、丁、戊、已、庚、辛、壬、癸。"地支"：子、丑、寅、卯、辰、巳、午、未、申、酉、戌、亥。And 天干地支rotate like生肖 so you can see "己" is the sixth one of 天干 and "丑" is the second one of 地支。Then you know which year it is referfing to.

这是“生肖”与“天干地支”的对应，2009 年是中国农历己丑（ jĭ chŏu）年。Hope to helps:)

生肖 is kind of like one of the 12 signs of the Zodiac, 十二生肖 literally refers to the particular 12 animals. In circular turn, the 12 animal rotate as years go by. Take 生肖together, though 生 means the year you were born, 肖 refers to the animal the year belongs to. 属相 means one of the rotating twelve animal you belongs to. The order of the twelve animals is fixed. And nearly every Chinese child learn to chant it since a very early age. 属相， 属means belonging to 相means picture, one of the 12 animals. One animal is one picture, right?