memes

That definition however does some weird things like saying that Tokyo and parts of Siberia are in North America, but Panama and Los Angeles aren't.

A continent is mostly just a social convention for a bigass geographic and geological structure that is above sea level and largely geologically and culturally separated. North and South America are connected by a land bridge, but that's really recent in evolutionary time and it's a real pain in the ass to cross. Europe and Asia are historically separated by the Ural mountains, but it's hard to look at them in modern day and say "these are two distinct landmasses" especially if you're saying India isn't, but historically getting from Europe to what's worth going to in Asia has involved crossing the Mediterranean much like getting to Africa or sailing around Africa in the early modern period. Australia is a giant landmass with not much else around as is Antarctica.