That's a loaded question there boyo! The more mechanics in play the less often skilled play is a useful descriptor (please, feel free, general reading populace, to ignore the loading of the word skill there, thanks). There's a scale in play here that takes some breaking down, and the results don't describe one gaming table, just a range of possibilities.
So, here goes - the goal of skilled play is for the players to be able to flex their creativity and problem solving (mostly) outside of rolling for effect X. Let's talk about the negative image first, just to make the positive easier to see. 5e has a lot of bells and whistles. It's perfectly possible (and fine) to run through whole sessions without doing anything but using spells and abilities as described in the rules to overcome obstacles. Obviously that's wrapped in some role playing, but there's no real movement outside the mechanics. An obstacle is presented, and abilities are consulted, rolled, and applied until the obstacle is overcome.
In a less mechanical environment, one where the solution to obstacles isn't so much a matter of apply skill or ability A, the player instead has to declare action X, wherein an attempt to overcome the obstacle is put in play but that is not reliant on skill or mechanic A. So player creativity and level of engagement with the diegetic gamestate is pushed to the front, above particular mechanical solutions.
Obviously, those are the extremes, and 5E, while it tends to the first, isn't entirely defined by it. I would contend that skilled play, in terms of 5E, is far more about the table approach than it is about the system. 5E can certainly trend the second way when players and GM are all playing with that as a desired gaming outcome, but it does take a certain level of commitment from the table.