Glossary
Rotate
In one line: Moving from one area of the map to another to help where it is needed.
What it means
Rotating means changing position: on defense, leaving your site to help the one under attack; on attack, shifting towards another site. Every rotation costs time and leaves the area you came from uncovered.
On defense it is one of the hardest calls: rotating too early opens your site (exactly what a fake punishes), rotating too late lets the other site fall. The basic rule: rotate on solid information (how many, where), not at the first noise.
An example
You are on B and hear three attackers, a smoke and a flash on A. Your teammate on A calls "three A, they're coming in". Now you have clear information: you rotate to A for the retake, while your anchor stays on B.