What is defined as a text for billing purposes?

G'day.... new inReach Mini user the past 24hr.

After a bit of a learning curve with the website I was finally off and running, and have been quite happily shooting out test messages to familiarise myself with the unit. My question is - what actually defines a 'text message' - is this an SMS sent out from a message, or a message composed on the mini, ie not a 'preset' message - I ask this because the preset messages are sent to phone numbers as texts - are these charged in the text allowance as well? This could be academic, I doubt we'll hit the 40 message allowance, and the overflow is cheap, I'm more curious.....

Cheers! and Merry Christmas......