1to count backwards (from 10 down to 0)
2to count down
3from the bottom (lines on a page)
4from the back (rows of seats)
Examples
tā他shì是dào shǔ倒数dì第sān三gè个dào到de的。
他是倒数第三个到的。
He was the last but two to arrive.
她总是在班上拿倒数第一。
She is always at the bottom of the class.
我是倒数第二个得知这个坏消息的。
I was the second to last person to hear the bad news.