WASP (White Anglo-Saxon Protestant) originally referred to the English, Scottish and Welsh immigrants that settled in and formed the bulk of the Colonial/Post-Independence American population, but due to immigration, the title of "honorary WASP-hood" was granted to German and Scandinavians among other groups.
So, it's...messy, but in general WASP in modern context would probably refer to basically "General White Americans" that are Protestant and of Northern/Western European-descent who don't really have a strong ethnic identity like Italian-Americans, Polish-Americans, Ashkenazi Jews, Criollo Spaniard Cubans, etc.
They are often referred to as the 'old immigrants'. WASPs originally came from northern Europe, especially from Britain, Ireland, Germany and Scandinavia. Immigrants from these countries continued to migrate to America throughout the 19th century.Sociologists sometimes use the term WASP to broadly include all Protestant Americans of Northern European or Northwestern European ancestry, regardless of whether they have British ancestry. The term is also used in Australia, New Zealand, and Canada.