Laravel中间件`throttle:api`是什么意思？

'api' => [
    // \laravel\sanctum\http\middleware\ensurefrontendrequestsarestateful::class,
    'throttle:api',
    \illuminate\routing\middleware\substitutebindings::class,
],

/**
     * /Illuminate/Routing/Middleware/ThrottleRequests.php
     * Handle an incoming request.
     *
     * @param  \Illuminate\Http\Request  $request
     * @param  \Closure  $next
     * @param  int|string  $maxAttempts
     * @param  float|int  $decayMinutes
     * @param  string  $prefix
     * @return \Symfony\Component\HttpFoundation\Response
     * 
     * @throws \Illuminate\Http\Exceptions\ThrottleRequestsException
     * 
     */
    public function handle($request, Closure $next, $maxAttempts = 60, $decayMinutes = 1, $prefix = '')
    {
        if (is_string($maxAttempts)
            && func_num_args() === 3
            && ! is_null($limiter = $this->limiter->limiter($maxAttempts))) {
            return $this->handleRequestUsingNamedLimiter($request, $next, $maxAttempts, $limiter);
        }
        
        // ....
     }