The point of origin is a symbol necessary for the dialing of Stargate addresses. While the first six symbols represent constellations indicating a point in space, this seventh point indicates where the wormhole is coming from. Milky Way and Pegasus Stargates each have a unique point of origin symbol, easily distinguished from the rest by those familiar with the technology. Destiny-style Stargates have a uniform design, and thus the point of origin can be any of the 36 symbols on the gate, depending on where it is dialed from.
For years, Earth's point of origin was unknown, as the Egyptians had placed two figures praying by the symbol of the pyramid. Daniel Jackson eventually recognized the mistake, and the Tau'ri were able to link to Abydos. (Stargate)
As part of a personal preference, when the point of origin hits the seventh chevron, Walter Harriman will announce "chevron seven locked", as a way to change things up. (SG1: "Children of the Gods", "Heroes, Part 1")
Known points of origin
Behind the scenes
After arriving on Abydos in 1996 in the feature film, Daniel Jackson had difficulty locating the planet's point of origin, despite that it would be the only different symbol on the gate. This can be contributed to differences between the film and series. In the movie, the Abydos Stargate had different glyphs than Earth's while in the series, all Stargates in the same galaxy have the same glyphs except for their unique point of origin. However, in the film, Abydos was also in a different galaxy.