Rock climbing topos have various standardized symbols, such as xx for a bolt anchor, or a dashed line for face climbing. In keys of symbols, I've sometimes seen SB defined as a "sling belay." What does this mean? Does it mean that there is a natural feature that you can throw a cordelette around and use as an anchor?
The glossary section of Big Walls by John Long and John Middendorf defines a sling belay as:
A hanging belay with no stance; listed as SB on topos
From perusing forums, I suspect this term arose during the golden age of Yosemite climbing, but was soon subsumed by the term "hanging belay". A Google Ngrams comparison gives a good visual of this.
This seems to matter more for big wall climbs, as using a sling belay is considered to be "aid". To climb such a route "free" requires a longer rope or adjusting the pitches to end at hands-free stances from which to belay. (This is from a US perspective, those in Europe may take a more relaxed approach to what is allowed for a free ascent.)
A sling belay is typically used to connect 2 points at an anchor.