1. A text is a continuation of signs that all belong to a font.
A font is a complete set of characters, by means of which we can compose a text. So, a sign is a character while it belongs to a font.
These characters can be drawn with a pencil or composed with any other mechanic or computerized way.
2. A text can be written out. In other terms, it is editable.
Whatever could be the material shape of a text: paper texture, font size, ink color..., we can change them, and the text will remain always the same one.
Handwritten, or composed in Helvetica or Palatino, a text never becomes another one -- and this is inherent to its nature.
3. A text is also the graphic transcription of speech. A text is always written in a natural language. Generally, we don't name "text" mathematical equations nor musical partitions, but, of course, there is not a clear frontier between mathematical, logical, programming, and natural languages.
Natural languages are characterized by a dual system of signs: one, sound, composed with phonemes, a second, graphic, composed with characters.
Every articulation of phonemes ought to be converted in readable types, and every articulation of types ought to be speakable in phonemes.
4. A text can be translated in another natural language. This is a corollary of the third proposition, saying that it is the visual transcription of speech. Another corollary of this assertion is that text can be translated in the same language. In other words, text is paraphrasable.
Then, text is a combination of characters (belonging to a font), which is editable, speakable and paraphrasable.
These four characterizations provide, I think, a complete definition of what a text is, but they contain many difficulties for a more accurate observation, and it is exactly what I shall do. Now, by means of this quadruple definition, it may be possible not to get lost.