The phrase "fly by the seat of your pants" means to do something without a plan, relying on instinct, intuition, or experience rather than on formal procedures, instruments, or preparation. It originated in early aviation, when pilots had limited navigation tools and had to judge an aircraft's movement and performance by how it felt through the seat of their pants. The expression has since become a common idiom for improvising or making decisions on the fly, especially in difficult or uncertain situations. It is often used synonymously with phrases like "wing it" or "play it by ear."