Acer spp. of the family Aceraceae. Native to North America.
"Ambrosia" is a term applied to maple when it has been infested by the ambrosia beetle. I do not know for sure if it is limited to any particular ones of the 60+ species of the genus Acer that are sold as various types of maple, but I do know that it occurs in big-leaf (aka red) maple (Acer rubrum) and that it is often listed as "wormy soft maple" (and A. rubrum is one of the two main maples listed as "soft maple", the other one being A. saccharinum) so generally I would expect ambrosia maple to be A. rubrum or A. saccharinum, but I doubt it is limited to those two species.
The fungus is eaten by the beetle and then gets into the tree sap when the beetle eats into the tree, and it spreads both through the worm-hole and up and down in the tree (carried along by the sap) and causes discoloring of the wood in streaks. It is these streaks which are so desirable to woodturners as it produces a beautiful pattern in the wood which is clearly seen when the wood is turned on a lathe.
This kind of insect attack / wood figure is not limited to maple, but that is the wood in which it is most well known.
The number of beetle holes will vary from very few up to what looks like a major infestation, as you can see from the pics on this page.
plank and closeup
some small planks cut from the big one directly above. Note that these appear more white, but that's just because the large plank had a mild patina and was a little dirty. These are freshly sanded.