preloaded mac dictionary

hello folks
I just wanna know which dictionary is used on OSx in the preloaded dictionary app?
in iOS when we define a word, we find oxford dictionary translating the word, so which dictionary is used on OS preloaded dictionary
another question, can I use voiceover on this dictionary to read word by word or line by line?, I've listened to the demo by David woodbridge about the dictionary and how to get the meaning of the word, but he didn't mention how to read word by word and so on
thanks

Forum: 

dictionary on the mac

to read character by character use the left arrow to go back a character and the right arrow to go right a character.
To read by word use option left arrow to go to the previous word option right arrow to go to the next word.

re: dictionary

thanks Isaac, but do you know which dictionary is installed on Mac? is it related to Apple or specified dictionary such as oxford or any other dictionary
thanks