What does it mean to "see the Dhamma" In a number of the books I'm reading on Buddhism, and in a number of talks I've heard on the subject, I repeatedly encounter the idea that the Buddha "saw the Dhamma" or that he "witnessed Dhamma" or the like. Other times, I've heard/read that the Buddha "saw" beings dying and taking rebirth, or that he "saw" the reality of anicca, dukkha, anatta, and the Four Noble Truths, etc. 

I'm having difficulty understanding what this all means. Is this metaphorical sight? Is it literal sight, in the sense of a vision or dream?

In terms of our own meditation practices, when we are told that we should "see" certain things, e.g. seeing a nimitta, should we expect something similar? Metaphorical "sight"? Literal sight? Something else entirely?
Thanks!
In "seeing the Dhamma", it's figuratively said, that is he witnessed for him self experientially the nature of reality, as opposed to intellectually understanding it. 


  "[A] monk who cultivates the Noble Eightfold Path, who assiduously practices the Noble Eightfold Path, comprehends with higher knowledge those states that are to be so comprehended, abandons with higher knowledge those states that are to be so abandoned, comes to experience with higher knowledge those states that are to be so experienced, and cultivates with higher knowledge those states that are to be so cultivated.
  
  What, monks, are the states to be comprehended with higher knowledge?
  They are the five groups of clinging. Which five? The body-group, the feeling-group, the perception-group, the mental-formation group, the consciousness-group...
  
  What, monks, are the states to be abandoned with higher knowledge?
  They are ignorance and the desire for [further] becoming. And what, monks, are the states to be experienced with higher knowledge?
  They are knowledge and liberation. And what, monk, are the states to be cultivated with higher knowledge?
  They are calm and insight."
  SN 45.159


As far as seeing other beings taking birth and dying, I don't have magical powers, but I understand this as being something like the eye of the mind expanding to actually witness this happening. With nimitas, they are lights that appear in the minds eye so are "seen" by the eye within as well.

Ajahn Brahm talks a lot about Nimitas