Service
also: services
A part of your system that does one job and that other parts ask for help, like a payment service or an email service.
A self-contained piece of software, often running as its own program, that provides one capability to the rest of the system through an API. It can be yours or third-party, like Stripe. In code, "service" also often just means a module grouping related logic.
In a restaurant, the kitchen, the bar and the dishwashing station each do one job. Waiters send requests to each and get results back without knowing how each station works inside.
Agents say "service" for two different things: a separate running program, or just a file of related code. Asking which one tells you whether a change adds hosting and deployment work or is only tidying code.
I moved the pricing logic into a PricingService in src/services/pricing.ts. It's still part of the same app, so there's nothing new to deploy.
When you say 'email service', do you mean a new separately deployed program or a module inside our existing backend? I'd like to keep one deployment if possible.
Assuming every "service" is a separately running program. Often it's just a code file that groups related logic inside the same app.