GSSP stands for Global Stratigraphic Section and Point. GSSPs are internationally agreed to reference stratigraphic sections representing the boundaries for paleontologic faunal stages. Since faunal stages do not cross geologic period boundaries, a subset of GSSPs define the boundaries of Geologic Periods and Epochs used on the geologic timescale. The effort to define GSSPs is conducted by the International Commission on Stratigraphy, a part of the International Union of Geological Sciences. The GSSP definition effort commenced in 1977. As of 2000, 37 of the 88 GSSPs required have been approved.

An ideal GSSP would

• be accessible by public transit from a major airport
• be accessible to research
• be extensive enough to ensure future access
• be easily related to other exposures worldwide
• contain a radiometrically datable bed at the boundary, and
• include well defined markers at the stage boundary that can be applied worldwide.

No GSSP is ideal.

The Precambrian-Cambrian boundary GSSP at Fortune Head, Newfoundland is a typical GSSP. It is accessible by paved road and is set aside as a nature preserve. A continuous section is available from beds that are clearly Precambrian into beds that are clearly Cambrian. The boundary is set at the first appearance of a complex trace fossil Trichophycus pedum that is found worldwide. The Fortune Head GSSP is unlikely to be washed away or built over. Trichophycus pedum is less than ideal as a marker fossil as it is not found in every Cambrian sequence, and it is not assured that it is found at the same level in every exposure. But no other fossil is known that would be preferable. There is no radiometrically datable bed at the boundary at Fortune Head, but there is one slightly above the boundary in similar beds not very far away.

Once a GSSP boundary has been agreed upon, a literal golden spike is driven into the geologic section to mark the boundary for future geologists. For this reason, GSSPs are also sometimes referred to as "Golden Spikes".