Definition of 'Spike'
1) The comparatively large upward or downward movement of a price or value level in a short period.
2) The trade order execution confirmation slip which shows all the pertinent data, such as the stock symbol, price, type and trading account information.
Investopedia explains 'Spike'
1) A good example of a negative spike in the financial markets is the infamous stock market crash of Oct 19, 1987, when the DJIA plunged 22% in a single day. There are plenty of more common, less drastic examples which are periodically seen in individual stocks when unexpected news or events, such as better-than-expected earnings results, reaches investors.
2) This usage originates from the antiquated practice of placing paper trade order slips on a metal spike upon completion.