The term "engagement" that is stored on the Contact record refers to historical campaign action data (opens, clicks, forwards, etc.) compared to the number of messages the Contact has received. This score is commonly used to identify Contacts that are most engaged vs. least (or not at all) engaged in the campaigns being received.
1. It is important to note that the Contact engagement score is an index or summary of combined actions, and not measured on a set scale (i.e. on a scale of 1-10).
2. It is also important to understand how different audiences or differing campaign types (i.e. informational vs. promotional) can return very different measurements of engagement. Compare "apples to apples" when using the campaign engagement score to draw conclusions of your campaign success.
3. There is no universal "right" or "recommended" engagement score, because not all accounts use all of the tracking features included in the formulas. But because the formula is the same for every Contact's interaction within an account, the engagement indexes are useful for comparisons to see which campaigns are performing the best.
4. If a contact's Tracking Preference is set to "Not Allowed", their engagement score will likely suffer as we are not tracking key behaviors to the score like opens and clicks. If you are creating a segment based on engagement, you may consider excluding users with "Not Allowed" tracking preference.