You shouldn't have been downvoted for that, it's a perfectly reasonable question. I had the same question myself.

Here's the funny part: there is no such thing as O(10,000) in big O notation. Big O doesn't concern itself with constant factors, it's about how performance changes with the size of the dataset. If two algorithms run in constant time but one takes twice as long as the other (maybe it's a debug build), they aren't O(1) and O(2), they are both O(1).

So it's not surprising that anyone would be confused by O(10,000). In big O, this would be an impossible value. It just wouldn't make sense.

The best solution, as always, is to use plain English. You will never go wrong by saying "about 10,000".

It's because the notation is pronounced "order of", which is also the vocabulary used when you do Fermi estimation: you don't care about exact numbers, but you want to guess the order of magnitude / power of ten correctly. It's linguistic overloading if you want.

I often see this used informally as shorthand for "on the order of", which is another way people say "approximately".

People, please stop downvoting this reasonable question