If you are one of the stalwart few who have not read any of the Harry Potter books, or caught any of the movies, a Portkey is an object that is magically endowed so as to become a conduit for travel. All one has to do is touch this object (an old boot, a trophy) and he or she teleports -- I think that's the right word -- across space to wherever it leads.
In other words, a portkey is a symbol. I touch the marble bookend on my shelf -- the one shaped like a horse's head -- and I'm suddenly 18 years old, just graduating high school and opening a package from my cousin Mary...and then I'm fifteen and Mary and I are riding my bay horse as he splashes into Deer Creek on my dad's farm.
I pick up the green glass frog sitting beside my coffee cup and suddenly I'm sitting in a room with several other writers doing an exercise...and then it's May, 2009, and I'm sitting on the back deck at my parents' farmhouse and I can hear the cricking of a frog...and then I'm a newlywed and very small treefrogs start appearing in our house (the front door didn't have a strip at the bottom to keep them out, yet).
Okay, so that's my fifteen minutes. I could say more.