The Full Form of LUT is Letter of Undertaking.

A letter of undertaking is a written agreement of terms between two parties. Most often, a contractor will write a letter of undertaking when hired to take on a project. It is a business agreement, and can be legally binding, so it’s important to clearly outline terms exactly as you have both agreed to. Briefly describe what the project is, what the cost will be, and any additional conditions you have agreed to. Also list any reasons either party would terminate the project early. Double-check that your letter is in business format, sign it, and send it.