[pps43]

Standard deviation is lowercase sigma, sum is uppercase sigma. They are not the same.

[klipt]

Uppercase sigma is used for multivariate distributions: https://en.wikipedia.org/wiki/Multivariate_normal_distributi...

[pps43]

But this is not common. If you don't know what uppercase sigma refers to, sum is a much better guess than standard deviation of multivatiate normal distribution.

In this case google is probably simply case insensitive.