Android facebook api: what is Android Key Hash?

When registering Facebook App, it requires you to type 'Android Key Hash'.
How to get Android Key Hash?

4 Prerequisites:
1. Must have Eclipse installed and android sdk installed
2. Locate 'debug.keystore' : usally at - C:\Users\(user name)\.android\debug.keystore
3. Locate 'keytool.exe' : usally at - C:\Program Files\Java\jre6 (your version)\bin
4. Open ssl: for 32 bit: here , for 64 bit: here.
    Extract to : C:\openssl

Now..

Type: keytool -exportcert -alias androiddebugkey -keystore C:\Users\Joshua\.android\debug.keystore | C:\openssl\bin\openssl sha1 -binary | C:\openssl\bin\openssl base64

type: 'android' for the password

That it!!