This question already has an answer here:
Inspired by Can you jump in combat?, along with answers and comments, where the assertion made by many seems to be "yes, you drop to the ground at the end of your turn." However, I'm not so sure it's that cut-and-dry.
The game organizes the chaos of combat into a cycle of rounds and turns. A round represents about 6 seconds in the game world. During a round, each participant in a battle takes a turn. (PHB5e p.189, emphasis in original)
It seems to me that the mental model of combat turns & rounds and standard initiative must be one of sequential declaration and resolution of simultaneous action: when I declare my movement and action(s) on my turn, I am declaring and my table is resolving those movements and actions I take during the round, all as a compromise between simulationism and table-speed.
By this interpretation there'd be nothing wrong with ending a turn mid-air, as no matter how many other declaration-resolution events came before my next turn, in-game zero time has passed between my character's end of one turn and the beginning of 's next. But that's just my interpretation--I'm sure there are good rationales behind others.
In case you're looking for a concrete example, here it is from last Wednesday: my STR18 gnome barbarian wants to long-jump that 15'-wide mud-river near Ogremoch's chamber. On his turn he disengages from a foe, runs 25' to the river, and jumps. His turn ends after 10' in the air. Next turn: is he in the mud trying to wade for 5', or is he flying through the air for 5'?
The clear answer for 3.5e: Is a character flat-footed if they end their turn mid-jump?