Something is jagged when it has an uneven edge or quality to it. Teeth can be jagged, saw blades can be jagged, and the edges of leaves can be jagged.
Jagged comes from 16th century English/Scottish and originally referred to a cloth, cut in a way so that the edge is not straight, but that is “toothed.” Imagine a tipsy seamstress trying to cut cloth in a straight line, but her sheers stray this way then that. She’s leaving a jagged edge on the cloth. Or perhaps you have a crush on the seamstress, but she is seen kissing another. Here, she’s leaving a jagged wound on your heart.