Hyphenation is the practice of connecting two or more words with a short horizontal line called a hyphen to create a single term or to show how words work together. When you write about a “well-known author” or describe something as “state-of-the-art,” you're using hyphenation to link words that function as a unit.

Hyphenation helps prevent confusion. Without it, “a man eating tiger” could mean a tiger that eats men or a man who is eating tiger meat, but “a man-eating tiger” makes the meaning clear: it's a dangerous tiger that preys on humans. Similarly, “twenty four hour shifts” is confusing, but “twenty-four-hour shifts” tells you exactly what's meant.

Some compound words always use hyphens, like mother-in-law or merry-go-round. The rules can seem tricky because they change depending on how you use the words. You might write about a fact that is “well known” when the phrase comes after a noun, but a “well-known fact” when it comes before.

At the end of a line of text, hyphenation also means breaking a word between syllables when there isn't enough space, placing the hyphen where the word splits: “hy-phen-a-tion” or “dic-tion-ar-y.”