Expiration Date or Exp Date will always display the date for the specific transaction you are viewing. Current Expiration Date will always display the date for the most recent Membership Transaction for this specific Constituent.
For example, If we are currently in the year 2020 and I am a member who purchased a 12-month membership on 2/1/2019. I then purchased a renewal on 2/1/2020. On the 2019 record, my "Exp Date" would be "2/1/2020" and that membership has expired but my "Current Expiration Date" would be “2/1/2021” as I have purchased a new membership since that original transaction.
You can always select Summary so that each member has a single row rather than the details of each purchase.