DC Check is a button that can be added to the page layout to show potential duplicate records for the record you are working on.
When viewing a record, you have the opportunity to check if there are any duplicate records already existing. If there are any, you can convert or merge them with the one you are viewing, instead of creating a new duplicate record.
After pressing the DC Check button, a search will be performed based on the applied Object scenario. All duplicates found will be shown on a detailed 'results page' with the opportunity to perform any deduplicate action.