The Toshiba TLP185(GR,SE is a single-channel DC-input transistor-output photocoupler in a 6-SOP surface-mount package. The output transistor is rated for up to 80 V and 50 mA continuous, with a typical Vce saturation of 300 mV.
The GR rank specifies a CTR of 100% to 300% at 5 mA forward current. This is a tighter and higher minimum than the GB rank (which starts at a lower percentage), so the GR variant guarantees a stronger output drive for a given input current. If your design relies on a minimum CTR of 100% to ensure the output saturates cleanly over temperature and LED aging, the GR rank is the correct choice. The GB rank may work in less demanding loops, but the GR gives more headroom.