In general, towns are smaller than cities. It is possible, though, to refer to a small town as a city, depending on context. (A small town might have a “city government”). Rarely, someone might refer to a city as a “town” in an ironic or metaphorical way.

It's very difficult, to be honest. The countries where English is spoken as a native language have different ways to define these. e.g. in the UK, 'city' is a legal designation - a settlement with a cathedral or a settlement given city status by the government. Added to this, some languages don't have two separate words for 'city' and 'town', different countries define populated areas very differently, and people's perceptions of 'big' and 'small' vary a great deal. I tend to go with big - city and small - town and let my students decide based on their perception of those words. But I also make sure they collocate correctly, e.g. always 'my home town' and never 'my home city's.

I agree with the other answers and this is generally the case: It is a question of size. However, in the UK, to be a city you need to have a cathedral, so if there's no cathedral, it is a town. This is why there are a number of towns in the UK which are larger than cities just because they do not possess a cathedral. An exception to this, was the town of Birmingham, which in the late 19th century was established as a city, although it did not have a cathedral at that time.

I had to think about this. I'd say a really small town would not be called a city. However a large city can be called a town. I'm thinking of 2 songs for example: "Chicago, Chicago, that toddlin' town." "New York, New York, it's a helluva town."

Just size and connection, town is smaller than city generally , and town is commonly subordinate to city in government organization structure. What do you think ?