What the less than symbol means
The less than sign < says the value on the left is smaller than the value on the right. 3 < 5 reads "3 is less than 5". It works for any kind of number: one half is less than three quarters, and minus four is less than one, because negative numbers sit further left on the number line.
The sign is a strict inequality, so 5 < 5 is false. If equality is allowed, use the less than or equal to sign ≤ instead: 5 ≤ 5 is true. In word problems, "fewer than", "below" and "under" usually translate to <.
The less than and greater than signs were introduced together by the English mathematician Thomas Harriot, in a book published in 1631.
The L trick and other memory aids
Tilt a capital L a little and it turns into the less than sign, so it is easy to remember as the sign for "less". The small pointed end always aims at the smaller number, while the open side faces the bigger one.
Reading from left to right helps too: if the first thing you meet is the point, say "less than". Teachers often add a hungry alligator whose mouth opens toward the larger number. The same rules apply to the greater than symbol, which is simply the same sign turned around.
How to type the less than sign
On US and UK keyboards, the less than sign is Shift + comma. For ≤, press Option + , on a Mac or Alt + 243 on a Windows number pad. On iPhone, tap 123 and then #+=. On Android with Gboard, tap ?123 and then =\<.
In LaTeX, type the sign directly in math mode, or use \leq for ≤ and \ll for ≪; MathJax and KaTeX also understand \lt. In HTML text, write < instead of the raw character, because a raw one starts a tag and can break the page. Our HTML symbol codes list covers the entity for every sign.
The less than sign outside math
In programming, x < 10 is a comparison. Every HTML tag starts with the less than sign, and websites use ‹ and « for back links because they look softer than the math sign. In code, the two characters <= stand in for ≤.
Type the sign followed by 3 and you get the classic text heart <3: seen sideways, the point is the bottom of the heart and the 3 forms the two bumps. Add a slash for a broken heart: </3. Want a real heart? Grab one from the heart symbol page.