It adjusts how the object opaque. 0 stands for perfect transparent (nothing can be seen), and 1 stands for perfect opacity.
Diffuse
It selects to what degree it makes the lighted area lighter.
Emission
It selects to what degree it makes lighter irrespective of how the object is lighted. It is also used an area light source in the path tracing.
Specular
It selects to what degree it makes the incident area of light lighter. It can be said in other words like speculum.
Specular power
It selects how wide or how small specular highlight is reflected.
Ambient
It selects to what degree it shows the color of the whole scene. It can be said in other words like environment light.
A global ambient color is specified in [Lighting Settings] by clicking the settings icon in the [View header > Disp > Lighting direction/color].
This example shows the case when the ambient light is bright red.
Reflection
Set the effect of reflecting light like a mirror on the surface of the material.
The item is applied for the ray-tracing rendering. It is not applied to the preview in this window, the 3D view and the scan line rendering.
Refraction
Specify the refractive index when light passes through a translucent material.
The item is applied for the ray-tracing rendering. It is not applied to the preview in this window, the 3D view and the scan line rendering.
It specifies the transparency of the material.
An alpha channel is used as an alpha mapping if the texture file contains it when you select [Texture] mapping and do not select [Alpha] mapping.
Bump
It specifies the irregularities of the material.
A bump map that indicates a height by brightness is shown if the specified file in [Bump] has 8-bit gray-scale. Otherwise, it works as a normal map that indicates a normal direction by RGB color.