Difference of toolchain recipes

It is a bit confused for the different recipes of toolchian, can somebody help to explain what's the difference for those recipes? E.g. gcc-cross, gcc-cross-canadian, gcc-cross-initial, gcc-cross-intermediate, gcc-crosssdk, gcc-crosssdk-initial, gcc-crosssdk-intermediate, gcc-runtime, etc. 

Is there any document for those description?


Best Regards,

Zhenhua