You can check to see which update channel you are currently using in File, Office Account (or Account in Word or Excel). Because this build is from the development branch, these users always be a version ahead of the official production release. There will be features available to users in the Insider ring that won't be available to Monthly Channel (Targeted) or Production.

Office Insider is a new level that delivers weekly updates from the development branch. These two are generally very close in terms of features and fixes.

Users in this ring will receive an update about a week before the official production release each month, and then the official production release when it goes out (2 updates per month). Monthly Channel (Targeted) is the original Insider program.