5,7,5 does not a haiku make.
A Freeform haiku doesn;t even need it at all.
Haiku is a classical japanes poetry form. To be a traditional Haiku, it must be:
Written in Japanese
Contain 17 things similar to syllables, but containing much less information.
Three lines.
One reference to nature other than human nature at least.
Contain a Kigo, or season word, usually in the first line.
Must end the first or second line with a breaking word (i.e not split a sentance across all three lines)
Must have some sort of unexpected twist in the last line.
Anglisced Haiku follow the same rules, but are written in ENglish, and use syllables, usually five-seven-vfive, though to be more acurate to the traditional form, one should use two stressed syllables in the first line, three in the second, and two in the third, with unstressed syllables adding to 12.
Freeform Haiku follow the same rules except for structure. They can be written in three lines with any number of syllables, or on one or two lines, or even four lines.
A Senryuu is a haiku in any other form, except rather than being about nature, it is about another subject. Often Human subjects are used in Senryuu.