Buy and hold
Buy and hold is a long-term investment strategy based on the view that in the long run financial markets give a good rate of return despite periods of volatility or decline. This viewpoint also holds that short-term market timing, i.e. the concept that one can enter the market on the lows and sell on the highs, does not work; attempting timing gives negative results, at least for small or unsophisticated investors, so it is better for them to simply buy and hold.
The antithesis of buy-and-hold is the concept of day trading, in which money can be made in the short term if an individual tries to short on the peaks, and buy on the lows with greater money coming with greater volatility.
One of the strongest arguments for the buy and hold strategy is the efficient-market hypothesis (EMH): If every security is fairly valued at all times, then there is really no point to trade. Some take the buy-and-hold strategy to an extreme, advocating that you should never sell a security unless you need the money.
Others have advocated buy-and-hold on purely cost-based grounds, without resort to the EMH. Costs such as brokerage and bid/offer spread are incurred on all transactions, and buy-and-hold involves the fewest transactions for a given amount invested in the market, all other things being equal. Warren Buffett is an example of a buy-and-hold advocate who has rejected the EMH in his writings, and has built his fortune by investing in companies at times when they were undervalued.
See also 
- Never Sell: Buy and Hold Forever (Efficient Market Canada, Investment Magazine)
- The Buy and Hold Apocalypse: Motley Fool article
- John Bogle, Bogle on Mutual Funds: New Perspectives for the Intelligent Investor, Dell, 1994, ISBN 0-440-50682-4
- Mark T. Hebner, Index Funds: The 12-Step Program for Active Investors, IFA Publishing, 2005, ISBN 0-9768023-0-9
- Interactive Java Applet "'Buy and Hold' - How much can you make over longer time periods?"