Layer Mapping & Antenna Ports in LTE PDSCH layer processing

I am reading LTE materials recently, and came across the antenna port term. I am quite clear about the term, however, what does a layer mapping exactly mean? Does ‘layer’ correspond to a logical channel/physical channel/communication pipe for the transmission of the modulated transport block (codeword) and mapping onto antenna ports?

I am providing references here.

I am also a beginner of LTE, which book is this LTE information?

See Page 141