Tens of thousands means 20 or more thousands. For example 50,000 is a number that is tens of thousands. It is a vague phrase meant to convey the order of magnitude of a number between 20k and 99k. It can be used to exaggerate such as when you want to say a lot but do not know the exact number.
As an example, here is a sentence in which there are many of something but it does really matter if the actual number is 20k or 85k: There are tens of thousands of mosquitoes in the park.
Here is an example using as hyperbole: There must have been hundreds of thousands of bats in the sky.
The word tens is plural so it implies 2 or more tens. It does not mean 10k exactly.
Photo example of with tens of thousands of soccer fans:
Hundreds of thousands.
Thousands of thousands.
Tens of millions.
Something like 20 or 50 or 80 thousand.
Unspecified large number
The wordcounter website has more info.