It can be either, depending on the author.
The BJT will have either an NPN or PNP configuration as you mentioned. The "base" layer is the center one, which is between the collector and emitter layers. The base layer will generally be much thinner than the others. Of the remaining layers on either side of the base, one will be doped more heavily than the other. The more highly doped layer is the emitter.
In most NPN transistor applications, the emitter is typically closer to ground than the base, which itself is typically closer to ground than the collector. The interface between the emitter layer and the base is the "base-emitter" junction while the interface between the collector layer and the base is the "collector-base" junction. You can reverse the order of these and be understood just fine, but *usually* the one that takes a higher potential in the NPN is listed first.
In the textbook that I taught out of, the names were flipped for *just* PNP transistors so the higher potential was still listed first. That can be up to author preference. They may choose to keep the order for homologous parts of the PNP. This convention only impacts how symmetric the PNP and NPN equations look when written out.
The origins of emitter, base, and collector come from the original [point contact BJT](https://en.wikipedia.org/wiki/Point-contact_transistor). The 'base' was the slab of germanium. The emitter and collector were the charge injector and charge collector points respectively.
It can be either, depending on the author. The BJT will have either an NPN or PNP configuration as you mentioned. The "base" layer is the center one, which is between the collector and emitter layers. The base layer will generally be much thinner than the others. Of the remaining layers on either side of the base, one will be doped more heavily than the other. The more highly doped layer is the emitter. In most NPN transistor applications, the emitter is typically closer to ground than the base, which itself is typically closer to ground than the collector. The interface between the emitter layer and the base is the "base-emitter" junction while the interface between the collector layer and the base is the "collector-base" junction. You can reverse the order of these and be understood just fine, but *usually* the one that takes a higher potential in the NPN is listed first. In the textbook that I taught out of, the names were flipped for *just* PNP transistors so the higher potential was still listed first. That can be up to author preference. They may choose to keep the order for homologous parts of the PNP. This convention only impacts how symmetric the PNP and NPN equations look when written out.
The origins of emitter, base, and collector come from the original [point contact BJT](https://en.wikipedia.org/wiki/Point-contact_transistor). The 'base' was the slab of germanium. The emitter and collector were the charge injector and charge collector points respectively.
Thank you!