Is the data definition for call log data available anywhere?

There is no single data sheet of call log data definition. But you can find lots of information about RingCentral call log data from the following links.

Call log interpret

Call log view

https://docs.google.com/document/d/1jd1B4E5gC_5Vepm1wRo5MjvdyN7ll1zRbB9AFToz1Q4/edit#heading=h.esmdkrf9cba6

https://medium.com/ringcentral-developers/visualize-your-business-communications-history-2c81f85c324a

Hope this helps. Let me know if you have question about a particular data field.

Sorry, I can't open the first two links. It says that the article is not made available in my country.