What is the number in square brackets?

In colours[1], what is the number 1, which picks out a single item by its position, called?

colours = ["red", "green", "blue"]
print(colours[1])

Why this activity was chosen

Bloom level: L1 Knowledge: Pick the correct technical term for a piece of code.
Block Model level: Atoms (step 1 of 4): individual syntax elements: names, operators, keywords and values.
Misconception targeted: shown after you answer, so it does not give the answer away.

Shared vocabulary is the foundation for everything else: students cannot explain, debug, or critique generated code (or specify what they want) without words such as parameter, index, key and iteration. Distractors are near-miss terms that novices genuinely confuse, such as parameter versus argument.

AI’s role here: AI may hint at what distinguishes two similar terms. It must not simply name the term, because recall is the skill being practised.