Bidirectional

-- Anti-Aliasing Settings --

Filter - 3 Anti-Aliasing reconstruction filters to use when resampling:

Min Sample - Number of samples to use on first Anti-Aliasing pass.
Pixel Width - Width of Anti-Aliasing pixel filter. [0-8]
Passes - Maximum number of Anti-Aliasing passes.
Inc Sample - Number of samples for additional Anti-Aliasing passes.
Threshold - Color threshold for additional Anti-Aliasing samples in next pass.

YafaRay Official Docs Bidirectional Pathtracing

-- General Settings --

Ray Depth - Amount of times that rays can be reflected in specular surfaces or pass through transparent surfaces.
Transparent Shadow depth - Amount of transparent surfaces that shadow rays can get through to find light sources.
Gamma In - The default gamma value for all colors, lights and textures.
This value is used to convert these values to linear color space used by the Yafaray renderer.
Gamma Out - The gamma value target for the rendered image.
CPU Threads - Number of CPU threads used by YafaRay. [-1] All threads.
This number should be equal to the number of CPU threads in your computer or minus one if you find that using all the
CPU threads bogs down your computer.
Normal Shadows / Transparent Shadows - Switches from Normal to Transparent Shadows.
Save Alpha - Exports an alpha file in addition to the RGB output file.
Z - Channel - Enable the Depth Channel in the output file.
Clamp RGB - Color depth is reduced to a low dynamic range before Anti-Aliasing filtering.

YafaRay Official Docs Render Settings

-- Output Render File --

View - If enabled YafaRay will render the Workspace view.
Camera - If enabled YafaRay will render the set Camera view.
Width - The width of the image rendered.
Height - The height of the image rendered.
> File name for rendered image output. This is where the rendered results will be saved.
Open Output Folder - Opens the folder entered into the above path.
Render - Exports XML file and spawns the YafaRay renderer.

YafaRay Official Docs Lighting Methods