So there is a few types of hashes you may come across, on most Unix type systems you could have a MD5 hash password file. But not just a MD5 hash, these will include a salt to make the hash unique.
Now other systems will use hashes, say like a web application. Now you could do these with a salt but many web developers ether don’t know this or assume that is already there, you can pick. With out the salt a string will always hash to the same result on every system, this is a problem. You could use something like a rainbow table, where you have a pre-hashed password list so you can quickly look up the password.