What does White ROM mean?

I want to get a Japanese phone from Amazon.co.jp because the phone is cheaper compared to eBay. (I know overseas can't really buy from amazon.co.jp but I can use a shopping service)

Some of the listings said that it's a White ROM phone. I looked up "White rom japanese phone" on Google and one of the search results said that White ROM means unlocked.
Is that true? I don't want to get a Japanese phone that's sim locked.

White ROM or Shiro ROM is a mobile phone with non registered, phone number, e-mail address or personal info. If you have a registered sim card, then you buy a white ROM with the same mobile company(Docomo, softbank or au), you can use the phone straight away.

Red ROM is a mobile phone which was stolen, illegally used or remaining outstanding debts. Once you use a red ROM, the access is automatically cut. All red ROM are recorded as illegal phones. There are many red ROMs among white ROMs. So be careful when you buy a white ROM.

White ROM means that a phone is unregistered and unlocked for the network that the phone was purchased for (docomo, softbank, etc.). It doesn't mean sim-unlocked, especially if you plan to use the phone overseas. Look for phones listed as "sim-free" instead.