The Difference Between High Tea and Afternoon Tea
To American ears, "high tea" simply sounds fancier than "afternoon tea". High tea sounds like something to dress up for, while afternoon tea sounds like a quotidian cup of Lipton in a wingback chair in your living room. In England, where both afternoon and high tea originated, it's afternoon tea that is the choice of the leisure class.
The name "high tea" wasn't a reference to the upper class, but most likely refers to the fact that it's traditionally enjoyed while gathered around a bar table or seated at a dinner table, rather than on a low armchair or couch. According to NPR's food blog, The Salt, high tea originated among the laboring class. Factory workers and office drones were frequently denied lunch breaks and would, naturally, be starving by the end of the day. They would rush out of their workplace to eat. They would take tea, along with quick foods like British savory pies, cold cuts, cheeses, and hearty hot dishes, which is how it earned its nickname of "meat tea". Today, high tea still usually takes place during those after-work hours between 5 p.m. and 7 p.m.
As for afternoon tea, The Salt cites Bruce Richardson' book, A Social History of Tea when they say that the practice started with Duchess Anna Maria Russell of Bedford who found herself hungry between lunch and dinner. She started having her staff whip up what amounts to a very refined snack time, around 3 or 4 p.m., which was late enough in the day to work up an appetite and early enough not to spoil dinner. She would drink tea and eat light finger foods like egg-and-cress or smoked salmon sandwiches (sans crust, of course) and bite-sized scones, tea cakes, and cookies. The duchess invited friends to afternoon tea and as soon as the word spread about this new hobby of the Downton Abbey-esque aristocracy, everyone wanted in on the sophisticated fun and it became the fashionable thing to do in the afternoons. Contrary to high tea, this new high brow activity was sometimes referred to as "low tea" because the upper class ladies and gentlemen would sip their tea from their bone china cups while sitting in comfortable low armchairs.
Due to its aristocratic roots, manners are of the upmost importance as part of afternoon tea. Put your napkin on your lap, stir your tea gently, eat daintily, and whatever you do, avoid crooking your pinky while you sip your tea or risk looking pretentious.