To understand the size differences: a Marklin HO scale locomotive is 1/87th the size of the real-world prototype it is modeled after; a Marklin Z scale locomotive is 1/220th the size of the prototype; and a Marklin 1 Gauge locomotive is about 1/32nd the size of the prototype.
Maerklin Z scale trains are also sometimes referred to as Marklin Mini-Club trains and also Marklin Spur Z trains .
As mentioned above, Marklin G gauge trains are also referred to as Marklin 1 guage trains and Marklin 1 scale trains and also as Marklin Maxi trains.
Marklin used to produce a line of HO scale hobby trains ("hobby" denoting less detailed than "model" trains) which were called Marklin Primex HO scale trains.