If you're not 'down with the cool kids' (a phrase which itself - ironically - declares me as NOT one of the cool kids!) then you may need some help deciphering slang you hear in town and online in chat rooms. Which is where the Urban Dictionary comes in. It's a crowd-sourced (and lightly curated) repository of slang and miscellany and... hard to access on mobile, since the web site's not responsive. So a client is needed and this is where this new UWP app for Windows 10 Mobile comes in.

From the brief Store description for UrbanDict UWP:

Universal Windows App for Urban Dictionary (Unofficial), and this is NOT a web crawler. Simple, nice, fast, and no-ads!

There's not much of a UI to show, but some screens by way of illustration:

On the left, the Edge experience of UrbanDictionary.com (even with the browser set to 'Mobile site') - on the right, UrbanDict UWP in action - very clear. 

More definitions, this time after a search ("troll"). Note that many of the definitions contain some adult material and I had to be careful what I screenshotting here! (right) the UI is limited to these basic controls on the '...' menu. 'Random', as it sounds, plucks something random from the database for you to use at the next cocktail party. Eh? What? They don't have those anymore? I'm out of touch.....!

It's not 100% clear how UrbanDict works - the developer makes reference to using space and bandwidth on the Azure cloud, so I'm guessing that a process at his end scrapes Urban Dictionary on the web and adds new content into a database online - which this client then accesses.

You can grab UrbanDict UWP in the Store here.