1 Your transaction may take a long time to move from the pending state to the confirmed state for the following reasons:  The wallet that the transaction originated from set a low fee on the transaction and has not been accepted by the Bitcoin network yet.
https://bitgo.zendesk.com/hc/en-us/articles/208332583-Why-is-my-transaction-still-PENDING-
1 The Bitcoin network could be under high contention due to high transaction volumes and so transactions can naturally take a long time to confirm.  If the transaction has been pending for longer than expected, check with the sender of the transaction to see if the fee set on the transaction was appropriate.
https://bitgo.zendesk.com/hc/en-us/articles/208332583-Why-is-my-transaction-still-PENDING-
The private key is another sequence of letters and numbers, but unlike your bitcoin address, this is kept secret. Think of your bitcoin address as a safe deposit box with a glass front. Everyone knows what is in it, but only the private key can unlock it to take things out or put things in.
http://www.coindesk.com/information/how-do-bitcoin-transactions-work/
1 The wallet that the transaction originated from set a low fee on the transaction and has not been accepted by the Bitcoin network yet.  The Bitcoin network could be under high contention due to high transaction volumes and so transactions can naturally take a long time to confirm.
https://bitgo.zendesk.com/hc/en-us/articles/208332583-Why-is-my-transaction-still-PENDING-
1 What can I do if my transaction has been pending for too long:  If the transaction has been pending for longer than expected, check with the sender of the transaction to see if the fee set on the transaction was appropriate.
https://bitgo.zendesk.com/hc/en-us/articles/208332583-Why-is-my-transaction-still-PENDING-
1 If transactions have less than one confirmation from the Bitcoin network, they are marked as pending.  The wallet that the transaction originated from set a low fee on the transaction and has not been accepted by the Bitcoin network yet.
https://bitgo.zendesk.com/hc/en-us/articles/208332583-Why-is-my-transaction-still-PENDING-
None of the transactions that she has in her bitcoin address are for that amount, and none of them add up to that amount when combined. Alice can’t just split a transaction into smaller amounts. You can only spend the whole output of a transaction, rather than breaking it up into smaller amounts.
http://www.coindesk.com/information/how-do-bitcoin-transactions-work/
Here’s what happens when you send Bitcoins to someone. Whenever you send someone Bitcoins, the transaction goes through different computers running the Bitcoin protocol around the world that make sure the transaction is valid. Once the transaction is verified it then “waits” inside the Mempool (i.e. in some sort of a “limbo” state). It’s basically waiting to be picked up by a Bitcoin miner and entered into a block of transaction on the Blockchain. Until it is picked up it’s considered an “unconfirmed transaction” or a “pending transaction”. A new block of transactions in added to the Blockchain every 10 minutes on average.
https://99bitcoins.com/why-bitcoin-transaction-pending-bitcoin-fees/
Last updated: 20th March 2015. Bitcoin transactions are sent from and to electronic bitcoin wallets, and are digitally signed for security. Everyone on the network knows about a transaction, and the history of a transaction can be traced back to the point where the bitcoins were produced.
http://www.coindesk.com/information/how-do-bitcoin-transactions-work/
1 An input. This is a record of which bitcoin address was used to send the bitcoins to Alice in the first place (she received them from her friend, Eve). 2  An amount. This is the amount of bitcoins that Alice is sending to Bob.  An output. This is Bob's bitcoin address.
http://www.coindesk.com/information/how-do-bitcoin-transactions-work/
what happens to pending transactions on bitcoin
On Bitcoin, if the transaction has been pending for longer than expected, check with the sender of the transaction to see if the fee set on the transaction was appropriate.