In the dictionary 'reality' is defined as 'the state of things as they are, rather than as they are imagined to be'.

defined 是动词 define 的过去分词形式。define 的意思是"下定义、界定"，由前缀 de-（表示"完全、彻底"）和词根 fin（表示"界限、范围"）组成，字面意思是"划定界限"。defined 在句中表示被动含义，指"被定义"的状态。