Considering the coronavirus will be with us for the foreseeable future, it’s good to have a grasp on the common terminology.
Phase 1, 2, 3…These refer to each country's plan to gradually reopen society. Typically phase 1 refers to total lockdown, followed by phase 2, which is an opening of certain sectors of society while maintaining strict regulations; such regulations may include capacity reductions in bars and restaurants, temperature checks before entering stores, and mandatory donning of masks and gloves. However, the important thing to remember is that while two countries may both call their new strategy "Phase 2," this can mean very different things.
Flattening the Curve: The purpose of flattening the curve is to avoid overwhelming healthcare systems by spreading the total number of cases out over a longer period of time. In the final analysis, it does not necessarily mean fewer people will be infected.
Contact Tracing: The purpose of contact tracing is to identify people who have recently been in close proximity with infected people, thereby alerting them that they are at higher risk.
How it works is pretty cool. For example, imagine I allow contact tracing on my iPhone. My iPhone will now send a random numeric code (by Bluetooth) to each mobile phone with which I come into close proximity with. All of my sent codes will be stored and attached to my account. Now, let's say that I test positive for Covid-19. Immediately, all of the phones which have received one of my codes will receive an alert, notifying them that they have recently come in close proximity with an infected person, and are thus at greater risk.
Mortality Rate: total number of deaths/total number of cases
The mortality rate has been difficult to calculate because the number in the denominator is missing most of the asymptomatic cases. We will likely not have a good idea of the true denominator until antibody tests are conducted across the country in random samples (like surveys), thereby giving us a good idea how many people have actually had it.
Infection Rate: The infection rate represents the number of people that an infected person infects. Thus, if I pass the virus to 3 people and you pass the virus to 2 people, the average infection rate between us would be 2.5.
Herd Immunity: Herd immunity is the notion that once a certain % of the population has contracted a certain virus, it becomes difficult for the virus to diffuse itself throughout the population. Immunity can either be achieved through vaccination or through natural immunity (i.e., by contracting the virus and recovering from it). While estimates vary, it is thought between 70-90% of a country’s population must be immune before herd immunity becomes effective.