What is ’ c ’ in here ?
They are specific coefficients for the given recurrence. for example, the fibonacci series is
f(n) = f(n-1) + f(n-2)… here there will be two coefficients (the 'c’s in the link) because nth term depends upon two terms, (n-1)th and(n-2)th terms. and for this series c1 and c2 are 1 and 1 respectively.
You could have other recurrences as well like f(n) = c1*f(n-1) + c2*f(n-2) + … and so on.