The travaux préparatoires (French: "preparatory works", in the plural) are the official record of a negotiation. Sometimes published, the "travaux" are often useful in clarifying the intentions of a treaty or other instrument. This is reflected in Article 32 of the Vienna Convention on the Law of Treaties (VCLT).
When interpreting treaties, the VCLT places this form of interpretation as secondary or less important than looking to the ordinary meaning (see Articles 31 and 32 of the VCLT).
The travaux are often available to the public on the websites created for a specific treaty (such as the Rome Statute) or on the United Nations website.
Source: UN Website