Basic Life Support (BLS) is a sequence of simple and effective steps to take when managing a first aid situation, specifically where someone has collapsed or there has been a bad accident. By following this sequence the first-aider will be able to deal with the most important issues first, and make informed decisions on the actions they should take and the best type of first aid treatment to offer.
Importantly, the sequence places the safety of the first-aider as the number one priority and ultimately gives the casualty the best chance of survival.
Note that while cardiopulmonary resuscitation (CPR) is a specific step within the BLS sequence, the sequence itself is sometimes referred to as 'the steps/guide to CPR' and/or the Primary Survey approach.
In an emergency, you are more like to to be treated by a family member, friend or colleague than a stranger.