# Definition:G-Delta Set

## Definition

Let $T = \left({S, \tau}\right)$ be a topological space.

A $G_\delta$ set (G-delta set) is a set which can be written as a countable intersection of open sets of $T$.

## Linguistic Note

The name $G_\delta$ originates from the German:

• G for Gebiet, which is German for area or neighborhood (here used in the sense open set in this case)
• $\delta$ (Greek d) for Durchschnitt, which is German for intersection.

## Also see

• Results about $G_\delta$ sets can be found here.