Kanji are characters in the Japanese language that originated from Chinese characters from the time of the Han Dynasty. There is some controversy about the history, but it is said that Buddhist monks brought the Chinese texts back to Japan.
In the Western world they are also known as symbols and ideograms, which, because of their beautiful calligraphy, have become very popular and used in tattoos.
Here are some popular kanji and their meanings:
Balance
Beauty
Believe
Courage
Destination
Dream
Eternity
Faith
Freedom
God
Happiness
Hope
Love
Luck
Peace
Success
Yin Yang
Zen
Here are some images of Kanji tattoos:
English 
Portuguese 
German 
French 
Spanish 
Polish