Hardwood flooring comes with either a flat square edge plank, or a beveled edged plank.  The beveled edge is usually noted as having a v-groove and varies in depth from manufacturer to manufacturer.  A shallow v-groove is often called an Eased-Edge. 

So what’s the difference?  The main advantage that beveled edge planks have over square edge planks is that they are more forgiving on uneven surfaces.  Because of this, you are less likely to have one plank sticking up higher than the plank next to it.  This alleviates the chance of kicking and splintering the wood through its lifetime. 

Beveled Edge Planks

As you can see, beveled edge planks have a very pronounced, deep inset groove.  They are more commonly seen in informal country décor.  The deep v-groove helps alleviate problems with sub floor unevenness that can cause discrepancies in the height between planks. 

Eased Edge Planks

A much slighter beveled edge than the deep v-groove, the eased edge planks help hide minor unevenness in the sub-floor.

Square Edge Planks

More commonly used in contemporary modern homes, square edge planks create a level surface that gives a formal feeling to the room.  Square edge planks are much easier to lay on sub-floors with no variation.