What's the difference between short-tail and long-tail keywords for Australian businesses?

In SEO, a keyword is whatever someone types into search. A root keyword is one word — "plumber." Short-tail is two or three — "commercial plumber." Long-tail is almost a sentence — "emergency plumber fix burst pipe in bathroom." A bank will always outrank a mortgage broker for "home loan" — but that broker can dominate "low doc home loans for tradies."