This refers to cpr. When performing CPR on an adult, one "cycle" is 30 chest compressions followed by 2 rescue breaths.
After this 1st cycle, the 2nd cycle starts, also with 30 chest compressions and 2 rescue breaths. In very specific circumstances (witnessed arrest, lay rescuer), CPR can be done without the rescue breaths i.e."hands only" cpr. Learn CPR through the american heart