What is the difference between a cosigner and secondary signer?

General explanations of what you may be trying to clarify:

Co-signer: Additional party who agrees to accept legal liability for a loan to strengthen the application submitted by someone else for credit. This person may have limited access to the account and transactions.

Co-borrower: Equal partner in the borrowing or using of the proceeds of a loan. Equal liability, equal benefit, equal account access.

Secondary Signer: Authorized agent on an account. This can be anything from an authorized user on a credit card (not liable for the account, user only), to a secondary authorized account member (checking, business accounts, stocks & bonds etc) who is able to initiate or approve transactions and have account access.