These are: The altered forms of some of the non-essential tones coincide (augmented eleventh with diminished fifth and augmented fifth with minor thirteenth) meaning those scale degrees are enharmonically identical and have multiple potential spellings.
The altered scale is made by the sequence: The abbreviation "alt" (for "altered") used in chord symbols enhances readability by reducing the number of characters otherwise needed to define the chord and avoids the confusion of multiple equivalent complex names.
The C altered scale is also enharmonically equivalent to the C Locrian mode with F changed to F♭.
[1] It is also enharmonically the seventh mode of the ascending melodic minor scale.
The added dissonance of the altered notes creates extra tension on the dominant.