Weak Market Efficiency
This says that all information that can be found out from looking at the movements in the past to the price of the currency or foreign currencies has already been taken into account.
And therefore it is fully reflected in the current price, so looking at that data to work out what will happen next may be a waste of time in that it's already factored into the price, to use the technical jargon.
However, there are many who disagree with this and believe that the use of charts and the like CAN be used to work out and predict what is likely to happen in the future with regard the price.
So the weak form makes a very interesting prediction that, if true, could lead to all those analysts losing their jobs - as it simply says you cannot say whether a currency is high or low based on comparisons with past data!
Related ArticlesThe Efficient Markets Hypothesis
Operating or Economic Risk
Foreign currency hedging explained
Semi-Strong Market Efficiency
What is an Efficient Market?