This is text that is left aligned and is the usual way that text is aligned. It's easy to read because every line starts against the left edge of the containing element and that's why it's the default setting.

This is text that is right aligned and it can be somewhat hard to read because every line starts in a different place.

This is text that is centered. Small blocks of text look good centered but it's hard to read large amounts of text as every line starts a different distance from the edge of the page.

Justified text is both left and right aligned at the same time. This is achieved by mathematically increasing word space on a line-by-line basis. This can result in gaps of white space (known as rivers) throughout the text, if the containing element is narrow or if there are multiple numerous extended consecutive occurrences of exceptionally lengthy words like these, so that only a few fit on each line.

A code example from Stylin’ with CSS, Third Edition by Charles Wyke-Smith. Visit stylinwithcss.com for more CSS information and updates.