[PHP] hash function secret

[Pablo Oliva]

I was reading the sept. issue of linux magazine and they discussed
security issues with web apps.
 
They mentioned that to generate signatures, you should include a secret
with your hash function:
s = S(m) = H(secret, H(m, secret))
 
What is the secret, just a sort of secret code that you include, like
some sort of random password: " gr8ckret46eme " as an example ???