In English, the word "发呆" is translated to "daydream". This word comes from the English verb "to dream", which means to have a series of thoughts, images, or emotions passing through the mind during sleep. "Daydream" specifically refers to a pleasant, imaginative train of thought that occurs while a person is awake and not paying attention to their surroundings.

Here are some example sentences:

She sat on the couch and stared out the window, lost in a daydream. (她坐在沙发上，看着窗外，沉浸在一个白日梦中。)

His mind wandered as he listened to the teacher, daydreaming about playing soccer. (他听老师讲课时，思维飘忽，梦想着踢足球。)

I often daydream while I'm working, imagining what it would be like to travel the world. (我经常在工作时发呆，想象着周游世界会是什么样子。)