Dip powder nails are somewhere between a regular mani and a fake acrylic nail. Instead of using UV rays to seal in your polish, the colour comes from a pigmented powder. Between base coats and a sealant, you dip your nails into a little jar of your chosen colour (SNS and Revel are the two most popular and vetted manufacturers) that could last three to four weeks.
The trend isn't exactly new per-se it's actually been around for years—but social media is quickly popularising the process and helping it stage a comeback. Over the past two years, more and more nail salons have started offering the service.