What is the difference between single sign on and open ID
openid, single-sign-on
Solution
"Singe Sign On" is a very general term. There are many ways to implement it, OpenID being one such way.
By "SSO" do you mean SAML SSO?
Refer following SO question for the difference between OpenID and SAML SSO:
What is the difference between OpenID and SAML?
Problem
As per my understanding OpenID and SSO is all about using a single identity to sign into many sites. so what is difference ?