In the Please Share web application, the Description field is where you can add an internal note explaining the context of a specific share request.
Content entered into this field will not be shared outside of your company. In other words, anything entered into the Description field will not appear on Twitter, Facebook, and/or LinkedIn (when team members share the content).
It is recommended that Please Share admin users include the URL of the content that they would like their team to share in the Description field. Doing so will generate a preview of the content when the share request appears in Slack. However, as of November 2021, including URL in the Description field is no longer required.