SWSE Statistics Page

I need your help, I'm trying to understand the Section Current sessions of SWSE Statistics Page, I understand its information about the current active sessions open, but I do not understand the descriptions count, mean, stddev

The documentation is described as follows but it is not very clear to me:

However, for an open session time event type, the statistics provide the following information:

• General statistics count.
• General statistics mean.
• General statistics standard deviation.
• Frequency mean.
• Frequency standard deviation.

  Regards.