Blockexplorer.com (S) Output is spent

[bitcoinbeamer]

Hello, when I copy and paste my wallet address on Blockexplorer.com and look at some of my transactions I see the (S) and when I mouse over it, it reads 'Output is spent'. What does that mean?

Looks like this right above the boxes that show the number of confirmations and the BTC sent:  0.3043 BTC (S)

Also, what does (U) output is unspent mean?

[achow101]

It means exactly what it sounds like, the transaction output has been spent or it has not been spent (unspent). Bitcoin works on transaction outputs, not addresses or balances of addresses. When you spend Bitcoin, you are actually consuming a transaction output. This is known as spending a previous transaction output. The coins that are spent go into new transaction outputs which are then spent by the receiver when they want to spend the coins.