Who's Waiting for a Transaction Confirmation Right Now?
Days of frenetic trading saw BTC drop from over $7,700 USD to $6,705 (at press time). It appears much of that value has gone to Bitcoin Cash (BCH/BCC) as disgruntled users appeared to abandon Bitcoin in the wake of the aborted "S2X" hard fork that attempted to increase block sizes.
Over that same period Bitcoin Cash rocketed from around $630 to over $1,000 (it's currently around $985). Suspecting a large-scale "flippening" of value from BTC to BCH, many users hurriedly sent their bitcoins to exchanges or quick trading platforms like ShapeShift, straining the network.
According to live data on Blockchain.info, there's currently (at press time) over 102,200 unconfirmed transactions, and over 100MB of transaction data in Bitcoin's "mempool". That's the repository of transactions broadcast to the network and waiting for confirmation. When you send a BTC transaction and it says "unconfirmed", the mempool's where it is.