A U-lock is a type of bicycle lock shaped like the letter "U." It consists of a solid metal shackle that secures your bike to a fixed object, making it difficult for thieves to steal. U-locks are popular among cyclists because they offer strong protection against theft, especially when used correctly with a sturdy bike rack or pole. To use a U-lock effectively, you should lock both the frame and one wheel of your bicycle to the object. This way, it becomes harder for someone to remove the bike. Many cyclists choose U-locks over other types of locks, like chain locks or cable locks, due to their durability and resistance to cutting.