In a question, an inclined surface is inclined at arcsin 1/3 to the horizontal surface. What does this arcsin 1/3 means?

arcsin = angle

Let, @ = arcsin(1/3)

@ = angle between hypotenuse and the horizontal surface.

Then sin @ = 1/3

As sin @ = opposite side / hypotenuse

we have hypotenuse is thrice the length of the side opposite angle @.

  An abbreviation for inverse sine.
 arsin(x) or arcsin(x) means the inverse sine of x, i.e. the number whose sine is x.
 Occasionally asin(x) is used to mean the same thing.

here its sin^-1(1/3)

arcsin is sin inverse.

theta = arcsin(1/3) means sin(theta) = 1/3

Just another way to write sine inverse.......