A Katydid is another name for a Bush Cricket.
Bush Crikets are somewhat similar in appearance to Grasshoppers, but
are more closely related to Crickets.
Easiest way to tell the difference is to look at the antennae,
these are fairly short for grasshoppers,
and conspicuously long for bush crickets.

They are not really the same thing, but there are occasionally instances in Science that a species common name inaccurately describes the species. A good example of this is my favorite bird of prey, the Peregrine Falcon (Falco peregrinus). Until sometime around the mid to late 1930's this falcon was known as a "Duck Hawk", it's not a hawk at all, it's a falcon. This is why scientist prefer to describe species by their scientific name. The term "grasshopper" is very generic, similar to the term "Fly" that can refer to one of hundreds of similar species. In general terms, The Katydid is of the family "Tettigoniidae", while (most) Grasshoppers and Locust are of the family "Acrididae"

They do not nest in the same manner, Tettigoniidae nest in plant tissue while "Acrididae" prefer soil and make really fun temporary pets for school projects ;-) I have included a link with a nice chart illustrating the differences (in very general terms) of what we commonly call "grasshopper" The link should answer most of your questions.... and hopefully inspire more questions........ Enjoy

www.ghorganics.com/page12.html