It doesn't translate well into English. Big Dipper Training Energy Fighting Seat. Basically, it means dojo.

For the anime english subtitles produced by Toei, Toei translated [北斗練気闘座] as "North Star Mind and Body Training Ground"

For Ken's Rage, it's translated as "Hokuto training field"

For Ken's Rage 2, it's retranslated as "Hokuto Chi Training Grounds"

I don’t exactly know the definition of Hokuto Renkitoza

But it’s a place of training any form of Hokuto no Ken

Yes there are many forms of it such as Hokuto Shin-Ken

Hokuto Ryuken etc