It means born into wealth. Commonly heard as "we weren't all born with a silver spoon in our mouths" - the wealth is symbolised by the use of silver in cutlery.

First, note that the correct expression is 'To BE born with a silver spoon (in your mouth), as in 'He was born with a silver spoon in his mouth'. Secondly, there aren't a lot of meanings for this idiom - there's only one, and all native speakers should know it. It means that a person comes from privileged origins, in terms of wealth and social class.

Be born rich, born in a noble family or with a great status.