1. Heart fail. This phenomenon happens when a person using an American keyboard attempts to create a heart by typing a less than sign, <, and a number 3 forgets to lift the shift key at the right time. The British variation looks like <£.
2. "I love you, but not enough to hit the backspace key and reattempt to create a decent looking heart."
3. A term coined by YouTube's jkimisyellow, it is is often used as a form of endearment with no hint of love.
1. "OMG ITZ UR 15th BIRTHDAY? HAAPPY BIRTHDAY <3<3<3<#<33<3<3<#!!!!!!!!!!11"
2. Me : Aww, you're so sweet <#
Friend : Fail.
Me : Heart fail. Dead.
An explosive expression of love, so explosive, in fact, that the author, eager to convey the sentiment, types so fast that they neglect to remove their finger from the Shift key prior to striking the 3 key, thereby resulting in the common typo <# instead of the intended heart.