Expressions used in Everyday Spoken English in Social and Professional contexts
If a place is teeming or swarming with something, it is considered to be full or almost full of that thing. Busy shopping malls might be teeming with people; just like airports, train and bus stations, etc. Similarly, if you say a place is 'swarming' with something, you are saying that those things are everywhere, like insects or ants, perhaps. 'Swarming' is more suited to flying or crawling creatures, but you might joke that the city was 'swarmed by' or 'swarming with' shoppers on Black Friday! These are informal terms that you will usually hear in relaxed or social situations, or with people you are comfortable speaking naturally with.