Can you explain the term due diligence?

Due diligence is a phrase denoting the process of verification and authentication of underlying information.  

Usually information is provided by one entity to another entity in order to do a high value transaction e.g acquisition of an entity or entering into a long term contract etc.

There are different categories of due diligence e.g Legal, financial, operational etc. Usually specialists undertake the due diligence effort. Legal due diligence will  be usually done by a law firm, Financial due diligence will be done by a auditing firm, operational due diligence will be done by industry technocrats.