What is dry insight? Following up from this answer - What is 'dry insight' exactly and how does it work. Is it a practice that someone will activity engage in or is it something that just happens to someone - a flash of inspiration out of the blue? I'm confused about how one could practice insight independent of any samatha practice if that is the meaning of it.
Dry insight or bare insight (suddha-vipassana) is the 'direct' way (Pali: ekayano maggo) to insight (nibbana), without jhana meditation practice (i.e. without 'upacara samadhi' or 'appana samadhi'). 

This direct 'momentary concentration' is called in Pali parikamma samadhi. This is the tradition of Mahasi Sayadaw; U Ba Khin and S.N. Goenka and others. The practitioners are called 'bare insighters' or 'dry' insighters.

You can find more information in 'The Progress of Insight (Visuddhinana-katha)' by Mahasi Sayadaw (1994): 'This approach to the ultimate goal of Buddhist meditation is called ‘bare insight’ because insight into the three characteristics of existence is made use of exclusively here, dispensing with the prior development of full concentrative absorption (jhana).’