Whatis the white wire and what is the black wire?

In normal wiring, black is the current carrying wire and the white is neutral. However, white can be used as a current carrying wire if retasked and properly marked.

Depends on the particular application. What voltage is present, and is it a switch leg?

I have a 2 circuit 3 terminal socket for a double lit lamp. The bottom part of the lamp has a black and white wire. The socket has two brown, one black and one white. Don't know where the black and white go.

Can you post a pic? Is it a single socket with 4 leads? And your 3 terminal seems to have 4 leads, making it a 4 terminal... Please clarify.

Are you located in the US or Canada?