it's not a question of terminology, there are 3 distinct tourist visa classes at the base level:
- Tourist Visa (TR), single entry aka SETV
- Tourist Visa Exemption scheme aka VE
- Tourist Visa on Arrival aka VOA
there is currently no 30 day tourist visa. SETV allows for 60 days, extendable once for 30 days at immigration office once you've been admitted to Thailand. it must be applied for outside of Thailand, usually in one's home country.
Visa Exemption means you can rock up to Thailand without a visa, so cheaper and less hassle; no pesky forms to fill out and no massive sticker in one's passport. us "Westerners" get stamped in for 30 days, extendable once for 30 days.
VE scheme isn't extended to all nationalities. however, in lieu of applying for a tourist visa beforehand, citizens of a handful of countries can get a Visa On Arrival. cost is B2,000 and it only as allows 15 days stay for tourism purposes, non-extendable.
however from 1 October 2022 the Thai government is temporarily extending the VE period from 30 to 45 days, and the VOA from 15 to 30 days.
that's the simple version. feel free to ask for clarification on any of the points.