For reference here is the definition of abstract character in Unicode 13
Abstract character: A unit of information used for the organization, control, or representation of textual data.
• When representing data, the nature of that data is generally symbolic as
opposed to some other kind of data (for example, aural or visual). Examples of
such symbolic data include letters, ideographs, digits, punctuation, technical
symbols, and dingbats.
• An abstract character has no concrete form and should not be confused with a
• An abstract character does not necessarily correspond to what a user thinks of
as a “character” and should not be confused with a grapheme.
• The abstract characters encoded by the Unicode Standard are known as Unicode abstract characters.
• Abstract characters not directly encoded by the Unicode Standard can often be
represented by the use of combining character sequences.