what does consolidation in trading mean?

Consolidation is when price is moving within a range or corridor just like water moving through a pipe. When consolidating, the price does not exceed a certain high/low price.

In investing, there's some thing called the "Dow Theory" which states that markets move in phases starting with the consolidation phase where sufficient momentum is accumulated to enable the market transform from a sideways movement to an actual upward or downward trend.