an app is literally just an app(lication) like any software you can get for a computer. It's just on ipads (and to a lesser extent on android devices) the market is tightly controlled, so you have to buy them online from Apple's appstore and install them from the ether. Tablet's do have limitations compared to a laptop, but they have strengths too. There's no tedious booting up, they're very light and use much less power. For browsing your usual sites it's actually much less hassle to use one. Some apps are useful. Addictive? I dunno, there was talk about candy crush and that game the developer withdrew, but I don't think that's an aspect of apps per se, more that people always have their phone with them and can become obssessive about stuff, whether social media or these games that reward regular visits, and try to encourage micro-purchases.