Letter spacing is the uniform amount of space added between all the letters in a piece of text, also called tracking. Unlike adjusting one pair at a time, it widens or tightens every gap at once to change how open or dense a word feels.
Imagine seats in a cinema row. Letter spacing is like deciding how much legroom every seat gets, applied evenly down the whole row, rather than moving one chair to fix a single tight spot. That single-pair fix is kerning, which is a related but separate adjustment. Open letter spacing gives uppercase labels and small captions a calm, premium feel, while tight spacing can make a heading feel bold and compact.
In CSS it is one property, letter-spacing, and the unit you choose matters. Using em ties the spacing to the font size, so a heading and its smaller caption keep the same proportional feel as the layout scales. Pixels stay fixed regardless of size, which is usually what you do not want on a responsive page.
Used well it sharpens typography. Used badly it backfires: too much space and a word falls apart into loose characters, too little and the letters smear together. All-caps text almost always benefits from a touch more spacing, because capital letters are designed to sit slightly closer than they should. The honest range is small. A value like 0.05em can transform a label, while anything past 0.2em starts to read as a gimmick rather than a refinement.
At TopDevs we set deliberate letter spacing on headings and UI labels so a client’s interface reads cleanly on every screen size, instead of leaving it to chance.
