bioRxiv is a preprint server, like Rxiv (for physics), medRxiv (for medicine), etc. 

In these preprint servers, researchers can upload their research manuscripts before they are peer reviewed.

This way, their results are there in the public domain as soon as possible, without the delay of sometimes months or years that takes to do the peer review and publication. 

Fore more on preprints and researcher's views on them see here.