USD Exchange Trade Volume is:
"A chart showing the USD trade volume from the top exchanges."
Based on that sentence
I'd assume that the blockchain.info company has chosen a set of exchanges (such as perhaps BitStamp, BitFinex, Coinbase, Circle, etc) that they have decided are the "top exchanges". Then they collect from each of their chosen exchanges the data that the exchange is willing to provide on the amount of USD that has been exchanged for bitcoins. The chart is then a representation of that data.
Estimated USD Transaction Volume is:
"The Estimated Transaction Volume in USD value."
Based on that sentence
I'd assume that the blockchain.info company is analyzing the bitcoin blockchain and attempting to guess which transaction outputs are the "amount transferred" and which are the "change". Then they are estimating a bitcoin exchange rate for the time that the transaction occurred. By multiplying their estimate of an exchange rate by their guess at which output is the amount transferred they arrive at an estimate of the USD value of the transaction. The chart is then a representation of that data as calculated for all transactions in the blockchain.
And one more. Where can i find info about volume of depositing money on bitcoin exchanges and withdrawals in USD?
Check with the exchanges. I'm not sure how many (if any at all) are willing to share this information publicly.
