Characters:  Depends on encoding.

ASCII:  7-bit  0-127, still so much of a standard that our keyboards are still based on it.

EBCDIC:  popular with IBM and nobody else.  IBM itself dropped EBCDIC early 2000's maybe?  8-bit 0-255 character set.  What was weird was that the alphabet was not contiguous.  The Character set had A-J then some other random symbols then more letters then more symbols etc.

Home computer revolution early 1980's.  Every computer had its own character set.

In modern times, we use Unicode, a 16-bit characgter set.  0-65535.  What are very useful symbols that don't appear on your laptop keyboard?  Emojis  Accented characters the Spanish "enyay" the German umlauted vowels, French "accent ague".  Chinese characters.  Greek symbols.

The cent sign.  The degree sign.

Strings are a sequence of characters.