NEF is an acronym for Notice of Electronic Filing.  An NEF contains:

• Case Number
• Case Title
• Date and time the document was filed
• The docket number of the document that was filed
• The docket text for that filing
• A list of parties who were served electronically

You will receive a copy of a NEF with each filing you send or bring to the court.  Each time the court files a document in your case you will receive a copy of that court-filed document and a NEF.