"Delta138" seems to be a keyword or code of some sort, but without context, it's difficult to provide a specific description. It could potentially refer to a flight number, a product model, a project name, or any other identifier depending on the domain it's used in. https://docs.google.com/document/d/1oFI2jnPPrqtSLJbgC-ArDs69B6ZaprLkOurgR4RMvGU/edit?usp=sharing