Quite a lot of difference Glen, though both are true oaks belonging to the botanical genus Quercus.
Tiger Oak is a form of our familiar native Oak (Q. robur). Occasionally growing trees become host to a type of fungus that turns the wood a rich brown colour which is what we refer to as 'brown oak' ).Sometimes the brown colour forms loose stripes along the grain and is referred to as 'tiger brown oak' or just 'tiger oak'
Holm Oak is a different species (Q.ilex) which is also called Holly-oak as it has thick, slightly spiky evergreen leaves. The wood is much harder than regular oak and fine textured as well. The two side-by-side look distinctly different.