The term "light rail" was apparently coined in the early 70's to avoid
the supposed stigma of the (USA) terms "trolley", "streetcar" or (Brit.)
"tram". Some operators of new systems do use the term "light rail" to
describe their routes.
On the other hand, the first new (and highly successful system) in the
USA was aptly named the "San Diego Trolley". Toronto's Spadina
Streetcar recently opened. And streetcars will return to Canal Street
in New Orleans.