What does 'Avg. removed per collection/category' in Dashboard mean?

Avg. removed per collection means the average number of 'Removed Products' which are not active or demoted in the set of collections or categories synced with Tagalys. 

e.g. you have 2 collections synced with Tagalys. Collection A has '0' products removed/demoted whereas Collection B has '10' products removed/demoted. The Avg. removed per collection is '5'.