An NDA, or non-disclosure agreement, is a legal contract where one or both parties agree not to share confidential information disclosed during a conversation, negotiation, or business relationship.
Most investors won't sign one before a pitch, since they see enough similar ideas that a blanket NDA would create legal risk for very little benefit to either side. It's still standard, and worth having, in conversations with contractors, potential acquirers, or partners who'll actually see sensitive technical or financial detail.
An NDA is only as useful as a company's willingness and ability to actually enforce it, which in practice means most of the real protection for a startup's information comes from being selective about who sees what, not from the document itself.
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