Hi everyone. Sorry for too many questions.

I searched a lot but I still can´t understand what form this sentence is.

Bu ne demek?

Why infinitive form"demek" has been used here?

Good question. I don´t have a good grammatical explanation. We just accept this.

In this context demek is not a verb it means ´meaning´. I´m curious now if there are any other cases something ending in ´mek´ or ´mak´ sometimes a verb and sometimes not.

It´s daily Turkish.

Bunun anlamı nedir ? = Bu ne demek ? = What does it mean ?

I think it is a short sentence from : Bu ne demek istiyor. So that can explain the infinitive.

Good luck