Range and Rows in window functions both work with ranges of lines?

Question

PostgreSQL

rows works with rows, while range works with a range.
What range are you talking about? I guess that the range is the rows in which the value (from the order by field) is equal to the value of the current row. If this is true, then what is a range here?:

count(*) over (order by test range between 1 preceding and 2 following)