In the context of Laplace transforms, what does the subscript in $h(t) = f(t)\cdot u_3(t)$ signify? **Problem** Note: I do not need help solving this problem (yet), but I'm unsure about notation. _Find the Laplace tranform of the function_ $h(t) = e^{2(t-3)}u_3(t)$. **Question** What does the subscripted $3$ in $u_3(t)$ mean?

As Dr. MV suggested in the comment, it referred to the right-shifted unit step function.

$u_3(t) = \begin{cases} 0, & t < 3 \\\ 1, & t \geq 3 \end{cases} $

_Posting this as an answer for the sake of completeness._