Wikipedias definition of inflation sounds exactly like op said and what I assume as well:

'In economics, inflation is a general increase in the prices of goods and services in an economy. When the general price level rises, each unit of currency buys fewer goods and services; consequently, inflation corresponds to a reduction in the purchasing power of money.'

I can afford less for the same unit of currency (Bitcoin) therefore I have inflation or deflation if I get more.

And people claim that Bitcoin is inflation save due to a limit amount of bitcoins being produced (I read that multiple times) while this is just not true.