No strategy: Investors who don't have a strategy have been called Sheep. Arbitrary choices modeled on throwing darts at a page (referencing earlier decades when stock prices were listed daily in the newspapers) have been called Blind Folded Monkeys Throwing Darts. This famous test had debatable outcomes.
Active vs Passive: Passive strategies like buy and hold and passive indexing are often used to minimize transaction costs. Passive investors don't believe it is possible to time the market. Active strategies such as momentum trading are an attempt to outperform benchmark indexes. Active investors believe they have the better than average skills.
Buy and Hold: This strategy involves buying company shares or funds and holding them for a long period. It is a long term investment strategy, based on the concept that in the long run equity markets give a good rate of return despite periods of volatility or decline. This viewpoint also holds that market timing, that one can enter the market on the lows and sell on the highs, does not work or does not work for small investors, so it is better to simply buy and hold.
Long Short Strategy: A long short strategy consists of selecting a universe of equities and ranking them according to a combined alpha factor. Given the rankings we long the top percentile and short the bottom percentile of securities once every re-balancing period.