Google API keys - What is server key and browser key

Question

I ma using google maps in my app, and use the URL as following format without the API key- values,

Answer 1

As of now (early 2018), I suspect the difference between server key and browser key is insignificant and only conceptual. Because the web console allows you to apply IP restriction or referrer restriction to any of your key. So, for the same key, you can apply a referrer restriction and then it works as a browser key, and you apply an IP restriction and then it works as a server key. Besides, I don't find specific documentation on server key vs browser key from this official help page.