The website Global Voices defines nommunication is a contraction of the Japanese word nomu ("to drink") and "communication":
Drinking with classmates or team mates when you are a student, or with colleagues when you are an employee is an important activity if you want to be part of the group. According to many, it is with a glass of beer or sake in hand that a new type of franker communication may occur, or a nommunication.
Nommunication (roughly translated as drinkommunication) is a term created by mixing the verb nomu (to drink) and the term ‘communication'. It can be defined as an important part of becoming a social person [en], as it deals with the working etiquette of an employee, and was created to indicate the type of communication that is established between a superior with his junior colleagues over social drinks apart from the office.
The blog Japan: A Conversation offers the following definition of nommunication:
“Nommunication” is a relatively recently coined Japenglish (hybrid Japanese-English) word that is a combination of the Japanese word nomu, meaning “to drink,” and the English word “communication.” Here (although not always), nomu specifically refers to drinking alcohol, and so this word in total refers to the communication between people who are drinking alcohol together. This most often applies to work parties (called enkai) that are nearly as obligatory as work itself.