Lomo is the traditional name in Argentina. Outside that tradition, butchers carry comparable beef cuts under different names — sometimes the same anatomical piece, sometimes a close cousin. The alternatives below are grouped by country so you can match what your local butcher actually carries.
Filet mignon is a steak portioned from the tenderloin — same muscle, with filet mignon specifically referring to the thick round individual steak cut.
Both come from the short loin but are very different eating experiences — tenderloin is butter-soft and lean while strip is firmer with more flavour and fat.