理解 (lǐ jiě) means to understand or comprehend, with a deeper sense of grasping meaning or empathising with someone's position. 理 means reason or principle and 解 means to untangle or explain. Together they suggest a reasoned, thorough understanding. It is more formal and emphatic than 明白 (míng bai, to understand clearly) or 懂 (dǒng, to understand / get it). It can also function as a noun: 表示理解 (to show understanding).