it seems wainscoting is a type of dado as dado neednt be made of wood. 

The term ‘wainscot’ originally referred to a superior quality of oak, which was the only type of wood deemed suitable to panel walls. The term ‘wainscoting’ as a type of wooden panelling is first recorded in 1570, though the first recorded use of a ‘wainscot’ as a wooden panel is in 1540.

The original purpose of wainscoting was to hide damp and mould from view in the interiors of affluent homes. As it was nearly impossible to damp-proof buildings prior to the 20th century, the solution was to hide the problem behind decorative wood panelling.
 

Right, not all paneling below the rail is wainscoting, in which case I find most people just say panel, though some say dado. I try to go with the terms used by the builder or client so as not to come off as correcting them, especially since I still have to think twice before pointing out a rail from a stile.