Invar is a nickel-iron alloy known for its unique property of minimal thermal expansion. This means that it expands and contracts very little when subjected to temperature changes, making it ideal for precision instruments and applications where dimensional stability is crucial. Developed in the early 20th century, Invar is commonly used in scientific instruments, clocks, and measuring devices. Its low thermal expansion coefficient allows it to maintain accuracy in environments with fluctuating temperatures, which is essential in fields like metrology and aerospace engineering.