Droplets are particles that break away from the main body of liquid in a Bifröst simulation. They have multiple uses, including artistic control, optimizing computation, and reducing simulation artifacts.
You can control the creation of droplets using Droplet Threshold and Mergeback Depth in the group of the main liquid properties. See Bifrost Emission attributes.
In addition, you can control how particles that have separated from the main body (not just particles that have exceeded the droplet threshold) get meshed using Droplet Radius in the Bifrost Meshing attribute group of the bifrostShape node. See bifrostShape attributes.