What is preparatory "it"?

[improvingMYenglish]

Hever you ever heard such expression? if yes what does it mean?
I've got this definition but in my opinion it isn't good as it doesn't explain me what exactlt this "it" is.

definiton: we sometimes ues the word "it" in odrer to prepare ouerselver for a phrase thich is going to follow.

 

[panjandrum]

It is the use of it at the beginning of a sentence.
It is a very common usage.
It is common in scientific/academic papers.

Have a look at BBC about preparatory it

You will also find this called "anticipatory it", and I'm not entirely certain, but I think this is the same as "cleft it".

Cleft sentences with WILL

BBC link on cleft sentences.