What is the difference?

In Europe I only know of houses/apartments (furnished or not) and hotels/motels (sometimes specialised in longer stays).

I take it the categories in Thailand are :

apartment = only the apartment as such (sometimes including furniture)

serviced apartment = apartment, always furnished, including cleaning, fresh towels, bed linnen etc. (same service as in a hotel?)

condo = apartment plus access to swimming pool, gym, .... (not serviced)

Is this about it? Or am I completely mistaken?

It's not about swimming pools. Condo is a building that is divided to units or "shares" and you can buy the "shares" so that you own a one unit of the condominium. Naturally you can also rent this unit from the owner if the owner so chooses to rent it out.

Apartments generally are buildings owned and managed by one company or individual. They come in two levels regarding service. With it or without it and actually you can get anything between no service to full hotel like service...

It's not about swimming pools. Condo is a building that is divided to units or "shares" and you can buy the "shares" so that you own a one unit of the condominium. Naturally you can also rent this unit from the owner if the owner so chooses to rent it out.

Apartments generally are buildings owned and managed by one company or individual. They come in two levels regarding service. With it or without it and actually you can get anything between no service to full hotel like service...

Although it seems as if Thais are more likely to refer to anything that is not a house or townhouse as a condo.

It's not about swimming pools. Condo is a building that is divided to units or "shares" and you can buy the "shares" so that you own a one unit of the condominium. Naturally you can also rent this unit from the owner if the owner so chooses to rent it out.

Apartments generally are buildings owned and managed by one company or individual. They come in two levels regarding service. With it or without it and actually you can get anything between no service to full hotel like service...

Although it seems as if Thais are more likely to refer to anything that is not a house or townhouse as a condo.

Not true. Before condo became a legal entity, there has always been flat and apartment (or mansion).

Problem now is, quite a few condo projects are designed and constructed as mansions, with some expensive finishes, and then sold as condo units. You can easily spot them out - long, dark and narrow corridors that lack natural ventilation and light, and with units' entrance doors facing each other.

With a condo you own a % share off ALL the assets including lift, fire fighting equipment, generator, swimming pool etc and oddly the land.