What is Amaterasu?
1.
The main goddess of the Shinto religion. Sun goddess.
Legend says that Amaterasu blessed the first emperor of Japan with a ruby (I think o.O I'm a bad Shinto *sighs*)
2.
Amaterasu (literally "Shining Heaven"), is a technique used by
Jiraiya: There is no escape. They're trapped in the esophagus of a fire-breathing rock toad from Myouboku Mountain.
Itachi: Amaterasu.
Jiraiya: ...!
See
3.
A move that Itachi uses that creates black fire that can burn through anything
Itachi uses amaterasu to burn through the frogs stomach that Jiraiya summoned around him
See