What is corrosion?Why does corrosion occur?List at least five types of corrosion?

 Corrosion is a big challenge in various fields, especially where metallic components are involved. 
 
answer the following and cite your references:

What is corrosion?
Why does corrosion occur?
List at least five types of corrosion?
Pick one type of corrosion you listed and do the following:

Explain its mechanism
Say where this type of corrosion is more likely to occur
Say what measures should be taken to prevent it

List your references