What is the correct notation for showing something is a union of many sets?

Question

If I wanted to show this would it look something like

Whatchamacallets = (Things + Stuff + Pandas)

Answer 1

If you're familiar with the indexed sum notation that looks like:

$$\sum_{i=0}^n x^2 + 1$$

There's a similar union notation.

$$\bigcup_{i=0}^n S_i$$