Computational model of biological object recognition
The question is resolved :

The name HMAX ( Hierarchical Model And X ) was coined by “Mike Tarr”, who wrote the “News and Views” accompanying the paper in Nature Neuroscience.

What was meant by Hierarchical?

The model has a hierarchical architecture : it contains different stages (layers). 

-- Increase in receptive field size and complexity in unit feature preferences along the
   hierarchy.

What was meant by X?

I think it is the pooling operation (it refers to the MAX).

Selectivity in S layer

The activity of each S unit is highest if all the afferents have the specified values.

Invariance in C layer

In contrast to S units, the C cells pool over their afferents, and the response is high if 
one of the afferents is high. This increases invariance if the afferents are tuned to the 
same feature, but at different positions or scales.