Break

Exits (terminates) a loop. Valid inside any kind of loop.

Break [, LoopLabel]

[AHK_L 59+]: If specified, LoopLabel identifies which loop this statement should apply to; either by label name or numeric nesting level. If omitted or 1, this statement applies to the innermost loop in which it is enclosed. LoopLabel must be a constant value - variables and expressions are not supported. If a label is specified, it must point directly at a loop command.

The use of Break and Continue are encouraged over goto since they usually make scripts more readable and maintainable.

Related

Continue, Loop, While-loop, For-loop, Blocks, Labels

Example

Loop
{
    ...
    if var > 25
        break
    ...
    if var <= 5
        continue
}

; Break the outer loop from within a nested loop.
outer:
Loop 3
{
    x := A_Index
    Loop 3
    {
        if (x*A_Index = 6)
            break outer  ; Equivalent to break 2 or goto break_outer.
        MsgBox %x%,%A_Index%
    }
}
break_outer: ; For goto.