KID: tactical, based on the..f5 lever, messy but in a good way for black.
Grunfeld [ also spelled gruenfeld]: based on attacking white's pawn centre and smashing it, usually with an early..c5 early on. More positional than the KID and less messy tactics.
Both are excellent defences. The above comments are generalities. Either defence can be tactical or positional in some lines.
If someone asked you to explain the two openings to him because he is torn about which opening to pick what would you say?