i'm gonna post something in here that i recentely posted in the Dashtalk forum so everyone reading this knows the difference between Instamine (also called Fastmine) and Premine :

Premine : Coins were given out before mining started. That means basically in the genesis block a certain amount of coins were distributed to accounts when the chain started.
In PoS coins, this is typically a 100% premine as all the coins are created at block 0. An popular example of this is NXT.
credits : SomethingElse

Instamine / Fastmine : is different and also has a much broader definition. That is when a cryptocurrency in its early hours / days / period due to either accidental fastmining (Dash) or intentional crippling of mining software (Monero) or 1 person / group ending up with a large number of coins (Bitcoin / Satoshi 1 million BTC) delivers a lot of coins in a select few hands.

The whole cryptocurrency scene could be seen currently as an Instamine to the outside world as only a small percentage of the human population is aware of it .. although the high Bitcoin price in 2014 and the media hype that followed after that could have changed that by now.