Horizontal boring mills come in two types - Floor type and table type.  Both will have a spindle that moves towards the part on a plane horizontal to the floor.  Most modern table type boring mills will be smaller tables with less weight capacity, but may have a rotation axis that allows them to turn and index like a lazy susan.  These are what the workpiece is fixed to.  Floor types are generally for larger pieces.  Some of them can run on rails that take up a whole room.

Another type of boring mill is the vertical boring mill, which is generally the same thing as a vertical turret lathe.  The difference is that the whole base of the machine will normally function like a chuck, rotating the part fixed to it to be turned (or machined in more modern CNC machines) and cut.

CNC Horizontal and Vertical boring mills cost more money, but has modern controls and programming.  The pricing difference can be enormous and will often not be justifiable if the customer is not a production or very high margin shop.  If manual, do they need a D.R.O. (Digital Read Out)- a DRO shows the position and if so, 3 or 4 axis?