Trading with price charts in the currency markets implies looking for repetitive shapes that happened in the past and by the time current price is making a shape like that traders have an educated guess about the possible outcome. This is what is known as a price pattern.
So looking for patterns when trading is one of the things that traders have in common as this helps forecasting price for the next period, depending very much on the time frame the pattern is being identified. If, for example, a head and shoulders pattern is identified on the weekly or monthly chart, then the measured move for it implies quite a strong move price will make.
When patterns are being used in combination with market psychology, the analysis becomes even more complex. It gives the trader a competitive advantage as, on one side, the pattern represents something from the past that can be projected into the future and on the other side market psychology comes to confirm/infirm that specific move.