3D Model - mechanim ready - what does it mean?

I am modeling, rigging, animating myself with 3ds max.

I was wondering, when people sell non-animated, but mechanim-ready models, what they mean by that?

How should a customer animate the models? Also, how can i create mechanim ready models with 3ds max?

Thanks in advance.

It means that the model has been rigged, and the bones of that rig are compatible with the humanoid avatar used by Mecanim. Therefore a customer can animate the model by assigning any animation clip they already own onto the model, and Mecanim will automatically re-target it appropriately.

This video is for Blender, but I guess the process for 3DS Max is probably similar: