What is dichotomous key?

Question

need 2 know.[duh...]

Answer 1

It is use to open the monotomous locks.

Answer 2

The dichotomous key is a reference tool that you can use to  identify species:

It is a succession of questions and each of them is a choice between two characteristics. Eliminating the characteristics that do not apply it leads progressively to the identification of the species.

Here is a site "How to Construct and Use a Dichotomous Key" which particularizes:

http://www.zoo.utoronto.ca/able/volumes/...