what does the word [n] mean in math

Hello!

For real number
the symbol means the integer part of i.e. the largest integer number not greater
than

In decimal notation for positive

For example,

 

For negative

if some numbers
aren't zero.

For example,

 

For any integer    

 

Sometimes this function is called floor function and is
denoted 

The ceiling function is defined as
the smallest integer not less than and is denoted