Open Rate

The percentage ratio of the number of opened messages to the number of messages sent. Open rate is a common effectiveness metric in email marketing and cold mailing campaigns.

Read also:

1. Email marketing

2. Conversion rate

3. Cold mailing 

Useful links:

https://en.wikipedia.org/wiki/Open_rate

https://sasdesign.pl/wskaznik-open-rate-go-zwiekszyc/

https://marketingdlaludzi.pl/wskaznik-open-rate-w-email-marketingu/