A tie in engineering is like a very strong and sturdy rope that is used to hold things together. Think of it like when you tie your shoelaces to keep your shoes from falling off your feet. A tie can be made of different materials like steel or concrete, and it is used to keep buildings, bridges, or other things from moving too much. It is like having a big hug around something so it doesn't fall apart or move around too much. Without ties, things might not stay together very well and could be dangerous.