|| - Logical OR Operator

An || (or) evaluates its left hand side. If it's falsey, it evaluates its right hand side and has that value. Otherwise it has the value of the left hand side. Its type is the union of the types of both sides.

You can think an || as syntax sugar of an if:

some_exp1 || some_exp2

The above is equivalent to:

tmp = some_exp1
if tmp
  tmp
else
  some_exp2
end