Showrooming is when a consumer goes into a retailer, shops for a particular item, says thank you and goes shopping online for the best price. This has been facilitated lately with the advent of smart-phone apps that allow you to scan an item's barcode and then have the app search for better prices, selection, and so on.
This is a toughie, but there's a certain Schadenfreude that a big box retailer like Target is complaining about comparison shopping.
Specialty stores like bike, golf and dive shops have for years complained about consumers walking in, picking the brains of the knowledgable and experienced staff, then walking out to shop online for their purchase. It drains sales and revenues from the community and puts it in the hands of corporate megaliths.
Of course, this takes that to a fractal plane...