By Contact Activity is a condition based on contact data to define logic which can be used in segmentation. By Contact Activity conditions would typically be a DateTime or Numeric type and are also often in aggregates i.e., maximum, minimum, count, sum, average, first, last.
When segmenting data, you will see the below standard conditions in the "By Contact Activity" drop-down list.
Examples of By Contact Activity:
Has opened email
Total distinct opens last X days...
Last open date
Has clicked an email link
Total distinct emails clicked last X days...
Last clicked date
Total distinct forms submitted last X days
Last submitted form date
Has received SMS
You can create customized By Contact Activity conditions if required, by consulting with a TractionNext developer which will then be added under "Custom" in the "By Contact Activity" drop-down list as shown below,