What does 'a touch of genius' mean? pls explain it to me, especially what 'touch' means in this phrase. Better add a few examples of this usage.
The phrase "a touch of" means a small but significant amount. For instance, someone might add "a touch of makeup" before going out, or a speechwriter might decide to revise a speech to add "a touch of humor". In both cases, the change is important, but not dramatic. Consider it in terms of cooking with a strong spice - you might add just a touch of pepper to make sure the dish is not too spicy.
This is also often used ironically, to mean a large and significant amount. For instance, a very drunk person who is obnoxious and loud might be described as having had "just a touch of whisky".
Finally, it can also be used in the abstract, to indicate some quality is present. "A touch of class" is a common phrase to describe something that is more elegant than usual. In that sense, "a touch of genius" means that the person (or organization, or project) has the quality of genius - in other words, is unusually clever, resourceful, innovative or surprising. Since we say that they have "a touch" of genius, we either mean that this is a small amount, or we are deliberately understating for effect.