# Defining a Multiloop

The term “multiloop” can mean different things to different people at first glance. The correct definition is “a loop with more than one stack coming out of it”, but some think that it is “a loop with three or more stacks coming out of it”, and some even define a multiloop using the terms “triloop” and “tetraloop”, saying it is “a hairpin with more than four unpaired bases”. This is so confusing! So it should be agreed that a multiloop is “a loop with more than two stacks coming out of it”; a loop with exactly two stacks coming out of it would then be called a stack loop (assuming the stacks are not adjacent; otherwise it would be a corner loop). Loops with only one stack coming out of them already have the name hairpin loop.

Freywa

Hi Freywa!

Yes, you are correct. A multiloop is a loop with more than one stacks comming out of it. For some of my strategies I have sort of redefined multiloop, as the strategies only counts for multiloops with three or more arms. But that definition only counts for that specific strategy.

Multi (loop) - means more than one string out of the loop.

And correct too:
A triloop is a hairpin loop with three unpaired bases. Not multiloop

A tetraloop is a hairpin loop with four unpaired bases. Not multiloop

I sort of like your term stack loop, for multiloops with two strings attacthed. We lack a term for this phenomena.

Corner loop/stack loop. Could you take a picture of those two different things?

I might put them in eterna dictionary then.

Hi all

Here are official definitions of different types of loops. (Degree means number of stacks coming out of the loop)