Undecided questions
'meri jaan' means 'my darling' . Is it true ??

jaan means 'life'(like plants have life).
so meri(my) jaan(life) may mean my darling depending on the context.

because

मेरी जान खतरे में है.
meri jaan khatare mein hai.

would more obviously mean 'my life is in danger' and not 'my darling is in danger'

Tushar explained it Perfectly :) Just a little extra note. There is a song I want to share that might help you to see the difference between Jaan as Life and Jaan as Darling

http://www.youtube.com/watch?v=onhMgSaYDeM

It says

Meri Jaan, Meri jaan ho tum - Darling you are my Life.
So First Jaan is In Terms of Dear
and Second is Life.

Hope it Helps :)