Thank you DdmrDdmr for the reply.
The Alexa chart is showing data delimited to the USA (not worldwide, unless someone has credentials to access and unlock information at other geographical levels).
Look at top of the chart. It says " In global internet traffic and engagement... "
So, Doesn't this mean that the visitors from all over the world have been considered?
Also, Alexa shows the visitors by country: (USA: 13.5%, India: 13%, Brazil: 8.9%). So, I guess all the countries are considered not only USA.
As per the above definition, your rank can decrease:
a) Because a given site receives less visits and/or page view.
b) Because other sites receive more visits and/or page views.
I completely understand you. A website rank does depend on traffic of other websites too.
But, when a website rank increases 500 in a day, can't we say that " The website traffic has been increased." ?
I think it's unlikely that traffic of 500 websites decreases at the same time.