What It Is: The percentage of email recipients who open a given email.
Most email marketers are still bent over backwards trying to optimize their subject lines for higher open rates. While this can have a positive impact -- and more opens are a great thing -- you should really be focused on optimizing the clickthrough rates, instead.
The fact of the matter is that open rate can actually be a misleading metric for a few reasons. Most importantly, an email is only counted as "opened" if the recipient also receives the images embedded in that message. Some percentage of your email users likely have image-blocking enabled on their email client. This means that even if they open the email, they won’t be included in your open rate, making it potentially an inaccurate and unreliable metric for Chapters, as it can under-report on your true numbers.
Note: You can get some value out of open rate as a metric if you use it as a comparative metric. For instance, if you compare the open rates of this week's email send to last week's email send (both to the same lists) it might give you some insight since the variables are somewhat controlled.