Old Order is the main, 'standard' Amish order. 200,000+ people. These are the Amish you picture: beard, black hat, gray buggy, kerosene lamp.
Rules
Buggy (no car). No grid electricity (gas, batteries). German in church. Clothing per Ordnung. 8 grades of education. Bundling allowed (or not — depends on specific community).
Where
Pennsylvania (Lancaster — the capital), Ohio (Holmes County — world's largest community), Indiana (Elkhart/LaGrange). Plus 30+ states.
Within Old Order
Hundreds of subgroups. Each community (30-40 families) has its own Ordnung. Lancaster Old Order allows gas fridge. Holmes — doesn't. One name — dozens of variations.