Client-Server: Browser (client) sends requests to server. Server processes and responds.
API: Interface for communication. REST APIs use HTTP verbs: GET (read), POST (create), PUT (update), DELETE (remove).
Database: Where data lives. SQL (PostgreSQL, MySQL) for structured data. NoSQL (MongoDB) for flexible schemas.
Load Balancer: Distributes traffic across multiple servers. Prevents any single server from being overwhelmed.
Cache: Stores frequently accessed data in memory. Faster than hitting the database every time.
Career Changer Tip: You don't need deep expertise. Understand what each does and when to use it.