One should look at pop as one looks at indie. They're two sides of the one coin, and the single broadest genres one can use to describe music. Both of them have very, very, very vague definitions that are largely down to the preference of whoever is using them, so a concise explanation of them is impossible. You can still use those two terms for their generally accepted "old" definitions: pop is popular, indie is unpopular. However, using the broadest possible terms is not usually ideal, and leads to stuff like RnB being submerged under both indie and pop in the present moment.
While a lot of people who hear music on the radio can have quite... uninformed (to say the least) definitions of pop and indie, most with sense generally identify pop as something with a straight-forward melody and production, sometimes accompanied by straight-forward lyrics (but not necessarily). The further away you get from the rigid straight-forwardness that defines POP, the closer you edge towards indie. Personally I would define Lady Gaga's 'Poker Face' as pop, but I would similarly define fun.'s 'We Are Young' as pop. It is as straight-forward as any Lady Gaga single, but many people think male singers + non-synthy production = indie, for whatever reason. In any case, I disagree with that.
True indie is a lot harder to provide examples for because well, it doesn't often make the charts. I'm sure most could pull any number of examples out but I'll go with stuff I'm playing currently: Purity Ring's
'Obedear' and perhaps Data Romance's
'She's Been High' (possibly the best song I've heard all year).
I feel like that post had a lot of filler surrounding a quite concise point, but basically just read the second paragraph and you'll find what you're looking for!