When you play hooky, you take the day off from what you're supposed to be doing. A man who goes to the beach instead of to his job at a bank decides to play hooky.
The classic example of someone who plays hooky is a kid who skips school, or is truant. You can also play hooky from any obligation, simply by not showing up. A bride might play hooky from her wedding, or a pilot could play hooky from work, leaving her plane sitting on the runway. The phrase comes from nineteenth century New York City slang, and it's thought to have its roots in the Dutch word hoekje, or "hide-and-seek."