While riding in a group you will hear warnings that tell you what is going on around you. Here are some your likely to hear:

“Car up”   

Car approaching from the front of the group.

“Car back”   

There is a car approaching from the rear of the group.

“Car right” or “Car left” 

A car is approaching on a cross street.

“Slow”   

The group is reducing speed. 

“Stopping”   

The group is stopping (generally for a stop sign or traffic light).

“Walker right” or “Runner right”

There is a pedestrian, on the right, that the group will be passing.

“Walker left” or “Runner left”

There is a pedestrian, on the left, that the group will be passing.

“Walker up”

There is a pedestrian on the road ahead.

“Rider(s) up”

There is a cyclist on the road ahead.

“Glass” “Sand” “Water” “Gravel” “Hole”

There is hazard on the road ahead.

Each cycling group has their own “slang”.  e.g. if “water” is called out, it can mean a pit stop for a drink to one group, while it might mean a water hazard on the road ahead to another group.