Conversion
Custom event
Also called named event.
Custom event is an event whose name and parameters the site defines. It records whatever your product thinks matters.
How it is measured
Choose a stable name, send it from code when the thing happens, and attach short data if needed. Names should be lowercase, descriptive and fixed.
Tarsier takes an event name up to 100 characters and optional data up to 500, and counts events separately from pageviews.
Worked example
A recipe app fires video_played, recipe_saved and share_tapped. Over a week recipe_saved sits at 920 while video_played is 3,100. A new share button adds share_tapped with 140 events in its first week.
The team sees that saving is more common than sharing and puts the save button first.
How it differs
A custom event is one you define. An automated event is detected by a script. An event is the general idea. A goal is a custom event you decided to track as a target.
Common errors
Renaming events in production. Putting personal data in the data field. Sending an event for every click. Using different names for the same action. Forgetting to test.
In practice
Write the event list in a shared doc with name, trigger and owner, and keep it short.