What did Jan share with Pam that was supposed to remain undisclosed?

The correct answer, "a secret," indicates that Jan shared information that was intended to be kept private. The nature of a secret inherently involves confidentiality, suggesting that it was not meant for others to know. This aligns with the expectation of discretion associated with secrets, emphasizing trust between Jan and Pam.

Other options such as "a plan," "a complaint," and "an invitation" do not carry the same implication of confidentiality. A plan could be discussed openly or shared in a more general context, a complaint may not necessarily require discretion, and an invitation is typically intended to be shared with the person intended to be invited. Thus, "a secret" is the only option that fully captures the essence of something meant to remain undisclosed.