Century

One hundred years.

The 1st Century was from the start of Year 1 to the end of Year 100
The 2nd Century was from the start of 101 to the end of 200
...
The 20th Century was from 1901 to 2000
The 21st Century is from 2001 to 2100

We are currently in the 21st century.

This is a 5 Dollar gold coin from 1855, which is in the 19th Century