Like the summation operator ∑, it is used to multiply some numbers regularly.
Write it as π a(k), where a(k) is a specific law, and k=m is written directly below π in small print, indicating that k starts from m; Just above π, write n in fine print, which means that it ends with k = n, and the result is a(m)*a(m+ 1)*...*a(n).
Among them, k can also be replaced by other letters, which makes no difference.
For example:
10
πn^2 = 1^2 * 2^2 *...* 10^2
n= 1