An acronym for "Not currently engaged in Employment, Education or Training". Originated from the United Kingdom. The demographic prevalence of NEETs is a serious social problem in Japan (among other places), where the term is typically used in a derogatory manner.
The lack of gainful employment can lead a NEET to social withdrawal, thus becoming a hikikomori. However, it is important when tagging to note that NEET and hikikomori are distinct, if related concepts.