[woodcote]

"What is HO?" was a very common question in the early days of Worthing HO Racing... And the answer means at least touching on model railway nomenclature. Most commonly these days, HO refers to half of O scale or O gauge. In English-speaking countries we do say aitch-oh. In other countries, the local equivalent of half-zero (eg ha' null in German) would be traditional in model railways, but for slot cars it would depend on the degree of American influence on that HO slot car community.

However, it's far from straightforward if you dig deeper into model railway scales and gauges. In the original 1900 Märklin model railways gauges, it was 0, 1, 2 and 3 - so H0 or half-zero is also correct. But then it gets extremely convoluted in terms of historical development and agreed standards - and we'll leave that nonsense to the model railway buffs...

In any case, most HO cars are between 1:60 and 1:70 scale - and 1:64 scale is sometimes used alongside or instead of HO on modern-day packaging. Even the earliest Aurora HO cars were designed to run with OO gauge UK model railways, which at 1:76.2 are significantly larger than the standard 1:87.1 scale of American HO model railways... 

A better question might be "Why are these 1:64-ish scale cars still called HO?" - and the answer is a story for another time... Maybe a thread in itself? And when someone asks the question on social media a link to the thread does the job. That's how Facebook and forums can dovetail quite nicely... Unless that dastardly Facebook profanity algorithm deletes the question :-)