I think the wikipedia page on the topic seems like a good definition to use as a rough guideline for the broad intent of the jam:
https://en.wikipedia.org/wiki/Puzzle_video_game
Puzzle video games make up a unique genre of video games that emphasize puzzle solving. The types of puzzles can test many problem-solving skills including logic, pattern recognition, sequence solving, and word completion. The player may have unlimited time or infinite attempts to solve a puzzle, or there may be a time limit, or simpler puzzles may be made difficult by having to complete them in real time, as in Tetris.
The genre is very broad, but it generally involves some level of abstraction and may make use of colors, shapes, numbers, physics, or complex rules. Unlike many video games, puzzle video games often do make use of "lives" that challenge a player by limiting the number of tries. In puzzle video games, players often try for a high score or to progress to the next level by getting to a certain place or achieving some criteria.