Why does running "echo $-" output "himBH" on the bash shell?

I'm using macOS. When I open a bash shell and execute echo $-, it outputs himBH. What does that mean?

What does $- mean in bash?

$- (dollar hyphen) bash parameter is used to get current option flags specified during the invocation, by the set built-in command or set by the bash shell itself.

What does echo stand for in bash?

Echoes (prints) the exit value for the previous command. If it failed it will be different than zero ( 0 ).

It shows your Builtin Set Flags. man bash then look for SHELL BUILTIN COMMANDS and then look for the set subsection. You will find the meanings of all those flags:

h: Remember the location of commands as they are looked up for execution.  This is enabled by default.
i: interactive
m: Monitor mode.  Job control is enabled
B: The shell performs brace expansion (see Brace Expansion above).  This is on by default
H: Enable !  style history substitution.  This option is on by default when the shell is interactive.