On type­writ­ers, the tab key moved the car­riage to a fixed hor­i­zon­tal po­si­tion, marked with a tab stop. This al­lowed typ­ists to cre­ate columns of text or num­bers, also known as tab­u­lar lay­outs (hence the name tab).

Tabs and tab stops still work the same way. A tab stop marks a lo­ca­tion; typ­ing a tab moves the cur­sor to that location.

These days, the tab is used only for in­sert­ing hor­i­zon­tal space in the mid­dle of a line. If you need hor­i­zon­tal space at the be­gin­ning of a para­graph, ad­just the first-line in­dent. For a true tab­u­lar lay­out, use a ta­ble, not tabs.

The tab is not as vi­tal as it once was, but word proces­sors still short­change its ca­pa­bil­i­ties. A new word-pro­cess­ing doc­u­ment has de­fault tab stops every half inch. These de­fault tab stops ex­ist so that some­thing hap­pens when you type a tab in the new doc­u­ment. But this de­fault be­hav­ior also sug­gests that what the tab key does is move the cur­sor a half inch at a time. Not true.

To get the most out of tabs, you should set your own tab stops. Avoid re­ly­ing on the de­fault tab stops—they un­der­mine the goals of con­trol and pre­dictabil­ity. As with word spaces, also avoid us­ing se­quences of tabs to move the cur­sor around the screen. 

To see your tab stops, dis­play the ruler.

With the ruler vis­i­ble, you can edit your tab stops.

The de­fault tab stop is a left tab stop, mean­ing text un­der the tab stop aligns to its left edges. Word proces­sors also of­fer cen­ter and right tab stops, as well as dec­i­mal tab stops that align columns of num­bers at their dec­i­mal points (see grids of num­bers for why this matters).

Use the proper tab stop for the job. For in­stance, don’t use a cen­ter tab stop to line up dec­i­mal num­bers. A right tab can be use­ful in a doc­u­ment footer to put two pieces of text (e.g., the doc­u­ment ti­tle and the page num­ber) at op­po­site ends of the same line.

Tabs are used in bul­leted and num­bered lists to sep­a­rate the bul­let or num­ber from the text. Tabs are also used in au­to­mat­i­cally gen­er­ated ta­bles of con­tents and ta­bles of au­thor­i­ties to put the page num­bers at the right edge of the table.

Tabs and tab stops have their place, but in most cases they act as a less-ca­pa­ble al­ter­na­tive to a ta­ble. Use tabs and tab stops if your for­mat­ting task is truly sim­ple. If not, up­grade to a table.