1.11Flow vs Subflow

You will encounter both.

Flow

Can have an event source:

HTTP Listener
Scheduler
etc.

Subflow

Reusable internal sequence of processors.

For example:

customer-flow
   ↓
validate-customer-subflow
   ↓
salesforce-customer-subflow

You might create:

subflow: upsert-salesforce-account

and call it from multiple flows.

Think of a subflow approximately like a reusable function.

async function upsertSalesforceAccount(customer) {
   ...
}