Instance vs Org vs App

Starting out with Salesforce brings with it a whole lot of new terminology. You might have heard words like instance, org, and app being thrown around. Often it feels like they are used interchangeably. Or do are they just general terms? Does it even matter? Let's get it sorted. No confusion. Nothing over the top. Just facts on facts.
  
Salesforce Instances, Apps, Orgs
  

Salesforce Instances

Salesforce Instances can be thought of as broad categories for Salesforce Orgs. There are two types of Salesforce Instances:
  1. Production. Either:
  • Essentials
  • Professional
  • Enterprise
  • Unlimited
  1. Development. Either:
  • Full copy sandbox
  • Partial copy sandbox
  • Developer pro org
  • Developer edition org
  • Scratch org
We won't be going into detail about the different types of sandboxes and production instances here (thank goodness). Let's save that one for your next cup of tea. The main takeaway here: Salesforce Instances are the biggest Russian Doll. Everything from here on goes inside an Instance of some kind.
  
Salesforce Org, App, Instance
  

The Salesforce Org

Our next smallest Salesforce Russian Doll the Org. A Salesforce Org (or Organisation) is your companies version of Salesforce and all of the data within it. It includes the users, data, custom fields, custom objects, automation processes, and Apex code corresponding to an individual organization. It is completely separate from all other Salesforce Organisations. Whether these are your own, or that of another Salesforce customer. Each org has a unique org ID which you will need to use if you ever contact Salesforce with issues about your org. You can find by going into:
  
SetUp > Quick Find > Company Information > Record page > Organization ID.
  

The Salesforce App

All right. Let's imagine that we are inside our Salesforce Org now. This is where you normally end up when you login to Salesforce. It's got data you recognise, settings you know, automation processes and systems that are specific to your company. A Salesforce App is a way of grouping related tabs and information in your org. As a Salesperson, you wouldn't want to be seeing all the accounting and finance data that only your companies Account Team needs to deal with. Likewise, they wouldn't need to see your Opportunity pipeline, or deal with Leads and Campaigns. We all know Salesforce can get busy, so Apps are around to separate data and functions in Salesforce based on categories of your choice. The easiest way to understand this is to check it out for yourself!
  
Salesforce Instances, Orgs, Apps
  
Salesforce Org, App, instances
In the top right of your Salesforce org, you will see what we call the 'Waffle Icon'. It's basically a little square of grey dots. Click on this to reveal a drop-down menu, then click 'View All' at the bottom to bring up the App Launcher. Volia! A full list of the apps available in your Salesforce Org.
  
  

An example to round it off

Let's say your company has:
  • 1 Production instance and 4 Development Sandbox instances. This means your company has 5 TOTAL instances.
  • Each instance will have its own unique org id (00D************)
  • Each instance can have it's own data and information - this includes different Apps. Your company (in this example), has a Finance App (for your accounting team), a Sales App (for your sales team), and a Marketing App (for your marketing department) in it's Production instance. Nice work!