When a new block of information has been verified for addition onto the blockchain, it has one confirmation. Each additional blocks added onto the blockchain gives the referenced block another additional confirmation.
The further back a block is on the blockchain, the more costly it becomes to reverse it (through malicious means). Block confirmation is typically used by crypto exchanges to consider a cryptocurrency transaction final to protect themselves against bad actors who aim to reverse transactions after depositing (known as double spending).
It is a bullish signal in technical candlestick pattern by comparing two lines of short-term moving average and long-term average. It is a golden cross when the short term moving average broke its long-term moving average.