Strand
Strands are flows of mana that connect the different Dimensions togther to form the Web of Worlds. There are two types of strands: Travel Strands, and Portal Strands.
Travel Strands are non-orbital intrusive: they generally remain outside the outermost orbital influence of a Dimension, and terminate in a Drop-off point. It is from this Drop-off that space vessels may enter/exit the Strand and use it to travel between the Dimensions. Travel by way of a strand is near instantaneous, but still does take time. As with travel by way of portal, travel on Strands is thus considered a method of dimensional folding.
Portal Strands are smaller capillary strands that finger off from Drop-off points and extend down to worlds within a dimension that are capable of supporting life. Portals were, up until the discovery and prevalence of space travel between Dimensions, the principal mode of inter-dimensional travel in the Core. The portal, it should be noted, is the feature that distinguishes Core from Fringe: the Core worlds of the Web are connected by way of Portals, but the Fringe worlds do not have portals and thus the only way to reach them is through space travel.
It should also be said that Strands of either kind are invisible to normal sight, as are Drop-off points up until the moment they are activated by a vessel's entering or exiting them. Portals, however, are always visible.