Definition:Repunit

Definition
Let $n$ be a (positive) integer.

Let $n$ be expressed in base $b$.

$n$ is a repunit base $b$ if all of the digits of $n$ are $1$.

When $b$ is the usual base $10$, $n$ is merely referred to as a repunit.

Linguistic Note
The etymology of repunit is obvious: it comes from repeated unit.