What is backend about ?
A: Data

Types: Document, Graph, Table, Dictionary, List, Array, Matrix

Boring Things

1. Caching
2. Authentication
3. Authorisation
4. Backup / Restore
5. System Administration and setup
6. Performance Tuning
7. Master Slave
8. Replication and Shrading
9. Middleware
10. Logging and Auditing
11. CRUD, BLOB
12. Transactions
13. Network Administration and setup
14. Long term Data Storage
15. Concurrency / Parallelism
16. Monitoring

Creative Things

1. System Architecture
2. System Modelling
3. Data Science: Crawling, Analytics, Statistics, Transformation, Predictions, Visual Modelling, …
4. Simulations

Good Overview

http://docs.python-guide.org/en/latest/