An explanation of the meaning of the fields given by 'getinfo' :
version - The version number of this bitcoin-qt or bitcoind program itself. Both of are equivalent. -qt is simply the graphical user interface version
protocolversion: The version of the bitcoin network protocol supported by this client (user agent software).
walletversion: The version of the wallet.dat file. Wallet.dat contains bitcoin addresses and public & private key pairs for these addresses. There is additional data on the wallet. Care must be taken to not restore from an old wallet backup. New addresses generated in the wallet since the old backup was made will not exist in the old backup! Source: https://en.bitcoin.it/wiki/Wallet
balance: The total number of bitcoins held in the wallet.dat file.
blocks: The total number of blocks which constitute the shared block chain.
timeoffset: Seconds of difference between this node's "wall clock time" and the median reported by our network peers.
connections: the number of peers on the bitcoin P2P network that this node is connected to.
proxy: If using a proxy to connect to the network, listed here, otherwise blank.
difficulty: the current mining difficulty factor. Difficulty is increased as more miners and more hash compute power compete to be the next one to have a block of transactions added to the blockchain.
testnet: Boolean value (true OR false). There is a parallel bitcoin network, the testnet, where trials and experiments may be carried out without impacting the official, live bitcoin P2P network
keypoololdest: timestamp (UNIX epoch) of the oldest key in the keypool
keypoolsize: A number of addresses are kept in reserve by the client. This is the size of that reserve.
paytxfee: Specifies what fee the client is willing to pay to expedite transactions. Miners may choose to ignore transactions that do not pay a fee, and these fee-less transactions will have low priority on queue of pending transaction and may linger there for hours.
errors: This field may inform of different status conditions. Full list of error codes in source file bitcoinrpc.h (https://dev.visucore.com/bitcoin/doxygen/bitcoinrpc_8h_source.html) (Examples: "Bitcoin not connected", "database error", "Keypool ran out"...)