Hello Healey
A streetcar could be a rail passenger car that runs on conduit power (underground pickup) like Third Avenue Railway System did in Manhattan because overhead wire for through-route trolley lines was banned in Manhattan NYC. Also in downtown Washington DC the streetcars ran on conduit underground power for the same reasons. There was a pair of channels in the center of both running rails that formed a slot for a "plow" board connected to the power truck to slide thru, and contact both the - and + rails in the conduit tunnel. CABLE CARS were also called streetcars --- cable cars being the predecessor of the conduit electric systems --- cable mechanism replaced by the underground slot "power and return" rails.
Thus a trolley car would be a streetcar that runs off overhead wire --- or trolley pole and pole-wheel (or shoe as wheels were sometimes replaced by) running on an overhead power wire --- as opposed to a "streetcar" which did not. However, uninformed or unsophisticated citizens generally called both vehicle types either streetcar or trolley car as common nature.
Similarly, Trackless trolleys are also called Trolley buses or sometimes plainly " the bus" or "the trackless" --- but rarely if ever called a streetcar or trolley as such.
By the way, the 3rd Ave EL (well, its rolling stock as well as other IRT , BMT and IND stock) still runs at my house -- see videos below;
https://youtu.be/t9HLG8a4F4Q (NOTE) A STILL PHOTO of an MUDC car is seen - Video scenes actually begins at counter mark 0:32 )
https://youtu.be/8Vat9puBusohttps://youtu.be/1hr_5_ni3v4https://youtu.be/llkmNtZ2LnMhttps://youtu.be/6JNbRRj4-j0https://youtu.be/BJKH3niTIDsTo see more of the entire layout & rolling stock, link below:
https://www.flickr.com/photos/44268069@N00/albumsregards - Joe F