Understanding the embeddings model (dunzhang/stella_en_400M_v5) by Alibaba. The details about the retrieve task and the s2s task

Question

The model I am talking about is hosted here: From the documentation:

We simplify usage of prompts, providing two prompts for most general tasks, one is for s2p, another one is for s2s.Prompt of s2p task(e.g. retrieve task): ..., Prompt of s2s task(e.g. semantic textual similarity task): ...

Question:

1. What is S2P task?
2. How is retrieve task different from semantic textual similarity task? Difference in the usage and also in the training steps would be much appreciated in the answer