Rag
The uneven edge unjustified text makes. A good rag wobbles gently; a bad one makes wedges, stairs and holes your eye follows.
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What it is
Rag is the uneven edge unjustified text leaves behind, normally the right edge of flush-left copy. Typographers judge it as a shape, not as individual lines. A good rag wobbles gently and irregularly. A bad rag makes patterns your eye starts reading instead of the words: deep notches, stair-step diagonals, near-triangles, or two consecutive lines ending at the same spot.
Every unjustified block has a rag, but you only ever hand-tune the ones people stare at: headlines, decks, pull quotes, taglines, hero copy. The tools are 'text-wrap: pretty' and 'balance', non-breaking spaces to glue short word pairs, the wbr element to mark a spot where a break is allowed, and widening or narrowing the measure by a couple of characters, which usually does more than any of them.
Gotcha: justifying the text is not the fix. Flush edges just move the unevenness inside the paragraph as rivers of white space, and on the web without decent hyphenation it gets worse, not better. Second gotcha: web rag is fluid. A break you hand-placed at 1440px becomes a stranded word at 390px, so fix the words or the measure rather than freezing the line breaks.
Ask AI for it
Set this article flush left with a ragged right edge and tune the rag: measure of 62 to 72 characters via 'max-width: 65ch', 'text-wrap: pretty' on paragraphs, 'text-wrap: balance' on headings, and 'hyphens: none' so no word snaps mid-line. Bind short function words to their neighbours in the headline and deck with non-breaking spaces so no line ends on 'a', 'to', 'of' or 'the'. Do not justify, and do not add manual line breaks.