Inline syntax

This is italic and so is this and this. You can also make an entire phrase into italics. Really though, italics are best reserved for the Titles of Books and Other Things. According to Grammarly , italics can may be used for:

1. Long written works
2. Periodical names
3. Moves, plays, and television shows
4. Podcasts and radio shows
5. Music albums, operas, and long musical compositions
6. Apps and video games
7. Works of art
8. Legal cases
9. Names of large vehicles (ships, aircraft, spaceships, trains)
10. Foreign words
11. Scientific names
12. When discussing specific words or letters
13. Unspoken thoughts and internal monologues
14. Emphasis

Of course when using italics to mark a title it should be not be intermixed with bold text or underlined text. The 15th edition of the Chicago Manual of Style says

All punctuation marks should appear in the same font – roman or italic – as the main or surrounding text, except for punctuation that belongs to a title or an exclamation in a different font. This departure from Chicago’s former usage serves both simplicity and logic.

There is little on when to use bold text and the little there is suggests that it’s valid in creative writing but otherwise should be avoided. Another suggestion was to use either italics or bold, but not both, and to make the choice based upon the type-face you have selected. The logic here is that some font-faces have a weak italic and so bold is a better substitute. Personally, I use bold sparingly, so I am not concerned about using it over much.

For expressing code, terminal commands, and other similar things we have inline code. This sets the font to monospace and usually adds some additional visual indicators.

def hello(name):
    return f"Hello, {name}"