Not a letter :p
No, it's a word!
a. the way in which we have communicated our discoveries throughout the history of humanity...
b. an alien language...
c. that which determines musical rhythm...
d. that which tells us how many of something there is...
It's like an 'expiration date' indicator.
The 2010 world average life expectancy at birth is 67.2 years.
But in the United States:
African Americans live 73.6 years.
Euro-Americans live 78.2 years.
Latino-Americans live 80.6 years.
Asian-Americans live 87 years.
its a part of life not many people understand
I don't know...but I know 1 is the loneliest number