What does these weird brackets mean?

[miregal]

 

[Zermelo]

You should really tell us the context in which they are used.

 

[pka]

View attachment 27305

I agree that you should give us the context.
However, I will tell that I have seen the symbol used for the greatest integer function.
But remember that is only a guess.

 

[miregal]

I agree that you should give us the context.
However, I will tell that I have seen the symbol used for the greatest integer function.
But remember that is only a guess.

You should really tell us the context in which they are used.

my teacher said that this means the value of [x] is the largest integer that is less than or equal to x, so pka's guess is correct, thank you both for your time