Definition of 'Market Timing'
1. The act of attempting to predict the future direction of the market, typically through the use of technical indicators or economic data.
2. The practice of switching among mutual fund asset classes in an attempt to profit from the changes in their market outlook.
Investopedia explains 'Market Timing'
Some investors, especially academics, believe it is impossible to time the market. Other investors, notably active traders, believe strongly in market timing. Thus, whether market timing is possible is really a matter of opinion.
What we can say with certainty is that it's very difficult to be successful at market timing continuously over the long-run. For the average investor who doesn't have the time (or desire) to watch the market on a daily basis, there are good reasons to avoid market timing and focus on investing for the long-run.