Imagine is a verb that means to form a mental image or concept of something not present to the senses.
Common usages of imagine include:
1. "Just imagine how happy she'll be!" (expressing hypothetical situations)
2. "I can't imagine why he did that." (expressing difficulty in understanding)
3. "You're imagining things!" (suggesting something is not real)
The word became particularly famous through John Lennon's song "Imagine", which envisions a world at peace.