Going Up, Down or Roundabout?

Today theme is: Stairs

These are not the stairs I wanted to take a picture of. We had planned to go on a harbour tour and I was going to nip to the Trinity Centre and take a photo of the stairs there that we have nicknamed Mount Trinity. But the weather put paid to that.

So these are different stairs.

The idea of stairs got me thinking though...

How many steps does it take to make a stairs? Ie. at what point, or rather what number of steps does it take to make stairs before you go from saying 'go up the steps' to saying 'go up the stairs'...3? 4? 5 or more?

And then a set of steps, whatever number, if they are outdoor can they be called stairs or are they simply steps no matter how many steps there are because they are outside?
Can a stairs only be found indoors?