Green Open Access (no cost, delayed)
Green Open Access research is published via the subscription model where a cost is charged for access, but it is also made available for free in an online repository after an embargo period specified by the publisher. Embargo periods differ depending on the publisher but can typically be between 6 and 24 months.
Publishers and journals vary in their policies about what can be made available via Green Open Access but in general it tends to be the Author Accepted Manuscript (the version that has undergone peer review but not yet been published).
The SHERPA RoMEO database provides details on individual journal and publisher policies on Green Open Access.