That's a very good question... and a question that I really wouldn't know how to answer...
There are many factors that affect what you would consider high traffic and in very specific niches 1000 per month would be considered high but... I'd say that 10000 per month is decent.
Before asking, do a search... if you don't find the answer, then ask The purpose of this forum is to help others in the community, that's why it's called Sitepoint and not Linkpoint. SP Guidelines - No fluff.
If your websites have huge amount of images and videos then you should expect more than 5000 unique visitors/ day.
How much big your websites(pages) are, you need to bring a volume of traffic which equals with your pages. And also it also depends on what product your website is concentrating with.
estimation for high tarffic volume of keywords, is depends on high quality of website and targetted keywords ( whether if it is local or global market )
As normal traffic volume estimation for a month is arround 800 -1000 is good