In one sentence, SLO is part of SLA. SLA is a legal contract while SLO has some specific definitions regarding performance, which can be used to guide performance testings.This topic is actually well discussed in the links below:

- [Differences between SLA and SLO][1]
- [SLA and SLO discussion on Quora][2]
- [SLA on Wikipedia][3]
- [SLO on Wikipedia][4]





  [1]: http://searchcio.techtarget.com/answer/Whats-the-difference-between-SLO-and-SLA
  [2]: https://www.quora.com/Whats-the-difference-between-Service-Level-Agreement-SLA-and-Service-Level-Objective-SLO-in-the-IT-industry
  [3]: https://en.wikipedia.org/wiki/Service-level_agreement
  [4]: https://en.wikipedia.org/wiki/Service_level_objective