Plain English Meaning
It is a way of pointing to one specific line going out from a navigation station. SXC is the name of the station, and R-084 means the line that runs out from it on a heading of 084 degrees.
Full Definition
A radial reference written in standard navigation shorthand, identifying the 084-degree magnetic radial from the SXC (San Marcus) VOR navigation facility. The three-letter identifier names the VOR station, and the 'R-' prefix followed by three digits names the specific outbound magnetic bearing from that station.
Context Anchor
Seen in instrument procedure descriptions and path-and-terminator leg examples, where a route segment is defined by a specific radial from a navigation facility.