They have minimum standards and then are also a bit overlapping. In my experience, I find the following accurate:

Full Service: Has a lobby, restaurant, bar, pool. Likely has room service, but that is changing. Likely had a lounge. Rooms are usually updated somewhat frequently and with high-quality finishings.

Courtyard: has a lobby and pool. Has the bistro, which is the lobby, restaurant, and bar. Bistro has morning and evening hours. Bistro food is decent quality. Rooms are updated somewhat frequently and with quality finishings. Has a couple suites. Small fridge in room.

SpringHill Suites: May have a small lobby. May have a pool. No restaurant, but may have a bar. Free breakfast buffet with fake eggs and tons of carbs. Rooms are updated less frequently and with lower quality finishings. Room has sleeping and sitting areas somewhat separated.

Fairfield Inn: Mostly the same as SpringHill Suites, but much cheaper quality on everything. Rooms do not have separate sleeping and sitting areas, but there may be a few suites. Rooms are updated infrequently. May have s microwave.

Residence Inn: Rooms can vary in quality from Fairfield to Courtyard, but generally are on the higher end of that spectrum. Rooms have separate sitting and sleeping areas. Many suites and maybe 2–bedroom suites. Full fridge, cooking area, and dishes. May have a pool. May have a lobby area. No restaurant or bar. Breakfast usually is fake eggs and tons of carbs, but is free.

TownPlace Suites: Same as Residence Inn, but on the lower end of quality and will smaller rooms, kitchens, etc. Expect ripped and burned furniture and stained carpet. Updated infrequently. Breakfast is cruddy prepared sandwiches in a microwave.