In mathematics, a cardinal number κ > א0 is called weakly inaccessible iff the following two conditions hold.
- cf(κ) = κ, where cf denotes the cofinality. Such a cardinal is called a regular cardinal.
- There is no next smaller cardinal number; i.e., for every cardinal λ < κ, there is another cardinal number between λ and κ. Such a cardinal number is called a limit cardinal.