The backticks (`) are a Markdown shortcut for what will later be rendered as <code> in HTML. Needless to say that this tag should be used to highlight actual code (or commands), not arbitrary words.
To highlight keywords, the <em> tag should be used. This again will often be displayed as italics, so you get the same result by wrapping text with <i> tags.
From the Chicago Manual of Style (chapter 7.47):
Use italics for emphasis only as an occasional adjunct to efficient sentence structure. Overused, italics quickly lose their force. Seldom should as much as a sentence be italicized for emphasis, and never a whole passage.
This is just general advice. Briefly looking over your posts, I don't even think that's relevant for you—but it might be for others. There's a certain trend where people use code for highlighting everything that could be remotely important.
See also: Inline Code Spans should not be used for emphasis, right?
