The flag of Denmark is a red field with an offset white cross. The offset cross is called a nordic cross, of which 5 country flags possess, Denmark being the first to adopt the style. The flag of Denmark is the oldest continuously used flag in the world and the date it was first used is not exactly known (back in the 13th century). The colors do not have specific meanings, just that the national flag has lighter red while the state flag has a darker red.
The Danish flag was adopted around 1219.