"Lap Harp" is a non-specific term used for the smallest harps, which can be held and played in the player's lap. There are an incredible variety of harp models, and lap harps
…are no different. There is an instrument called the "Melody Lap Harp", another by the same manufacturer called "Music Maker Lap Harp." They both have 15 strings, but they hardly count as harps (which by definition don't have a sound board behind the strings.) These meet the definition of psaltery or dulcimer. There are many versions which are more serious and which have more strings, going all the way up to professional hammered dulcimers (with tripled strings) and which are "lap" harps only in that one side rests against the legs while the main weight of the instrument is supported on one or more legs. Proper harps have a soundbox which is the connection point for one end of the strings, and a harmonic arch which is very nearly parallel to the strings. Supported on these is the tuning rail with the bridge pins, sharp/flat or sharp levers or sliders or rotaters (they can be quite clever!) and the tuning pegs which anchor the other end of the strings. Laps harps which are proper harps generally run from 22 to 27 strings, in gut, nylon or metal. (MORE) 
