Custom Links were first available in v8 for GP and continue on in v9. A custom link let you associate a link with an item in GP. For example, you can associate a bank website with a checking account. Then, when you click on the hyperlink to the account, you get a choice to go to the external link or the account in GP.
Dynamics GP comes with an option named "Custom Links" which can be found under company setup, this can help out user to navigate and perform some additional task right from GP for the respective entity such as Bank Accounts to online banking page, Vendors portal, items catalog, Tracking Number links on the shipping method etc.
To setup custom links, lets consider an example of online Banking page linking with Bank Account. Step 1:
-Setup Custom Link (Microsoft Dynamics GP menu >> Tools >> Setup >> Company >> Custom Link)