Group Policy and Security Policy are two things.

GPO, Group Policy or Domain Group Policy are the same thing. It is implemented in Windows AD environment.
http://technet.microsoft.com/en-us/library/cc725828(v=WS.10).aspx

Local Group Policy (gpedit.msc) is a version of Group Policy. We use Local Group Policy to manage stand-alone computers because they are not in domain. Please note that if a computer is in a domain and a conflict occurs between domain and local policy, domain policy override the local policy.
http://technet.microsoft.com/en-us/library/cc775702(v=WS.10).aspx

Then, Security Policy (secpol.msc) is another story. It mainly focus on security.

The difference between Security Policy and Group Policy is that Security Policy are some security related policies pre-defined in Windows. While Group Policy is blank when you create a new one and you need to edit it and apply it to a user group or computer group. That's I can think of and hope it helps.

  Group Policy forum