Some common issues addressed in an NDA include:[3] outlining the parties to the agreement; the definition of what is confidential, i.e. the information to be held confidential. Modern NDAs will typically include a laundry list of types of items which are covered, including unpublished patent applications, know-how, schema, financial information, verbal representations, customer lists, vendor lists, business practices/strategies, etc.; https://en.wikipedia.org/wiki/Non-disclosure_agreement

So yea, it literally has everything to do with clients, corporate secrets, customer lists, etc.

Nondisclosure agreements are one of the best ways to protect trade secrets -- valuable confidential information that businesses want to keep under wraps. That information could be a sales plan, a list of customers, a manufacturing process or a formula for a soft drink. By using a nondisclosure agreement, you can ensure that your secrets stay secret -- or have legal recourse if they are misused or disclosed to the wrong parties.

A nondisclosure agreement -- also called an NDA or a confidentiality agreement -- is a contract in which the parties promise to protect the confidentiality of secret information that is disclosed during employment or another type of business transaction.

https://www.nolo.com/legal-encyclopedia/nondisclosure-agreements-29630.html