Glyph
A glyph is the graphic representation of a character, for example a letter, a number or a punctuation mark. Therefore, depending on the used font one and the same letter can have a different look. Think on the character A in Times New Roman, Comic Sans, Arial or Courier New.
A character simply refers to the abstract idea of a character, which reveals nothing about the look and the typographical graph. This graphical representation becomes visible through a glyph defined in a font.
Therefore, Unicode is simply a code that stands for a certain character, and does not yet say anything about how the specific characters will look later in a document or on a website. This requires a font file, in which there are glyphs assigned to the corresponding Unicode code points. But there is no font on earth, in which all Unicode code points have representations (see fonts for that). In this case, another font can be used instead for this character or the character appears as a box.
The format respectively the encoding used for the underlying text file or document is also irrelevant with regard to the glyph(s) used. It doesn't matter whether a text is encoded in UTF-7, UTF-8, UTF-16, UTF-32 as little endian or big endian or even as ASCII or ANSI text. In any case, each character in the text is first transferred to its associated Unicode Code Point, regardless of its previous encoding. For the same character, this code point is always the same regardless of the encoding used. This is the only reason why we see the same text in a text editor when we look at files with different encodings but with the same content.