“Data skew” is a condition which you will encounter when working for a big client where there are over 10,000 records. When one single user owns that many records we call that condition ‘ownership data skew’.
Data skew in Salesforce happens when large number of child records (more then 10k) are linked to one parent records.
Data skew primarily refers to a non uniform distribution in a dataset. … The direct impact of data skew on parallel execution of complex database queries is a poor load balancing leading to high response time.